doc: GSG tweaks for DX

- mention usefulness of a fast computer for improving build time
- move Ubuntu boot USB drive earlier in the list of prereqs
- move some sentences around for clarity
- improve appearance with some more spacing after images

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/getting-started/getting-started.rst

@@ -34,7 +34,8 @@ Before you begin, make sure your machines have the following prerequisites:
 
 * Hardware specifications
 
-  - A PC with Internet access
+  - A PC with Internet access (A fast system with multiple cores and 16MB
+    memory or more will make the builds go faster.)
 
 * Software specifications
 
@@ -46,13 +47,13 @@ Before you begin, make sure your machines have the following prerequisites:
 * Hardware specifications
 
   - Target board (see :ref:`hardware_tested`)
+  - Ubuntu 18.04 bootable USB disk (see `Ubuntu documentation
+    <https://ubuntu.com/tutorials/create-a-usb-stick-on-ubuntu#1-overview>`__
+    for instructions)
   - USB keyboard and mouse
   - Monitor
   - Ethernet cable and Internet access
   - Serial-to-USB cable to view the ACRN and VM console (optional)
-  - Ubuntu 18.04 bootable USB disk (see `Ubuntu documentation
-    <https://ubuntu.com/tutorials/create-a-usb-stick-on-ubuntu#1-overview>`__
-    for instructions)
   - A second USB disk with minimum 1GB capacity to copy files between the
     development computer and target system
   - Local storage device (NVMe or SATA drive, for example)
@@ -101,7 +102,9 @@ To set up the ACRN build environment on the development computer:
    .. code-block:: bash
 
       sudo apt update
+
       sudo apt upgrade -y
+
       sudo apt install gcc \
            git \
            make \
@@ -124,7 +127,8 @@ To set up the ACRN build environment on the development computer:
            bison \
            xsltproc \
            clang-format
-      sudo pip3 install lxml xmlschema
+
+      sudo pip3 install lxml xmlschema defusedxml
 
 #. Install the iASL compiler/disassembler used for advanced power management,
    device discovery, and configuration (ACPI) within the host OS:
@@ -165,7 +169,7 @@ target hardware.
 You use the **board inspector tool** to generate the board
 configuration file.
 
-.. note::
+.. important::
 
    Whenever you change the configuration of the board, such as BIOS settings,
    additional memory, or PCI devices, you must
@@ -358,14 +362,14 @@ Generate a Board Configuration File
 Generate a Scenario Configuration File and Launch Script
 *********************************************************
 
+You use the **ACRN configuration editor** to generate scenario configuration files and launch scripts.
+
 A **scenario configuration file** is an XML file that holds the parameters of
 a specific ACRN configuration, such as the number of VMs that can be run,
 their attributes, and the resources they have access to.
 
 A **launch script** is a shell script that is used to create a User VM.
 
-You use the **ACRN configuration editor** to generate scenario configuration files and launch scripts.
-
 To generate a scenario configuration file and launch script:
 
 #. On the development computer, install ACRN configuration editor dependencies:
@@ -383,14 +387,7 @@ To generate a scenario configuration file and launch script:
 
 #. Your web browser should open the website `<http://127.0.0.1:5001/>`__
    automatically, or you may need to visit this website manually.
-
+   The ACRN configuration editor is supported on Chrome and Firefox.
-   .. note::
-
-      The ACRN configuration editor is supported on Chrome and Firefox.
-
-   The browser-based configuration editor interface:
-
-   .. image:: ./images/gsg_config_01.png
 
 #. Click the **Import Board info** button and browse to the board configuration
    file ``my_board.xml`` previously generated. When it is successfully
@@ -399,6 +396,8 @@ To generate a scenario configuration file and launch script:
 
    .. image:: ./images/gsg_config_board.png
 
+   |br|
+
 #. Generate the scenario configuration file:
 
    a. Click the **Scenario Setting** menu on the top banner of the UI and select
@@ -406,10 +405,14 @@ To generate a scenario configuration file and launch script:
 
       .. image:: ./images/gsg_config_scenario_default.png
 
+      |br|
+
    #. In the dialog box, select **industry** as the default scenario setting and click **OK**.
 
       .. image:: ./images/gsg_config_scenario_load.png
 
+      |br|
+
    #. The scenario's configurable items appear. Feel free to look through all
       the available configuration settings used in this sample scenario. This
       is where you can change the sample scenario to meet your application's
@@ -427,6 +430,8 @@ To generate a scenario configuration file and launch script:
 
       .. image:: ./images/gsg_config_scenario_save.png
 
+      |br|
+
    #. Confirm that ``industry.xml`` appears in the directory ``/home/<username>/acrn-work``.
 
 #. Generate the launch script:
@@ -436,21 +441,29 @@ To generate a scenario configuration file and launch script:
 
       .. image:: ./images/gsg_config_launch_default.png
 
+      |br|
+
    #. In the dialog box, select **industry_launch_6uos** as the default launch
       setting and click **OK**.
 
       .. image:: ./images/gsg_config_launch_load.png
 
-   #. Click the **Generate Launch Script** button.
+      |br|
+
+      #. Click the **Generate Launch Script** button.
 
       .. image:: ./images/gsg_config_launch_generate.png
 
+      |br|
+
    #. In the dialog box, type ``/home/<username>/acrn-work/`` in the Source Path
       field. In the following example, ``acrn`` is the username. Click **Submit**
       to save the script.
 
       .. image:: ./images/gsg_config_launch_save.png
 
+      |br|
+
    #. Confirm that ``launch_uos_id3.sh`` appears in the directory
       ``/home/<username>/acrn-work/my_board/output/``.
 
@@ -483,8 +496,8 @@ Build ACRN
       make olddefconfig
       make -j $(nproc) targz-pkg
 
-   The build can take 1-3 hours depending on the performance of your development
+   The kernel build can take 15 minutes or less on a fast computer, but could
-   computer and network.
+   take 1-3 hours depending on the performance of your development computer.
 
 #. Copy all the necessary files generated on the development computer to the
    target system by USB disk as follows: