doc: simplify navigation with restored doc org

A few more tweaks to the site navigation since we moved the content back
to its original folder structure.

Remove the temporary "doc reorg in progress" banner.

Add reference to hardware in the "try" section.

Add link to the documentation home page in left nav pane.

Add additional redirects to handle external links to moved content.

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

doc/contribute.rst

@@ -0,0 +1,46 @@
+.. _contribute_acrn:
+
+Contribute to ACRN
+##################
+
+Here's where you'll find details about ACRN's high-level design and
+design principles, along with guidelines followed by the
+development team. With this information, you too can contribute to the
+project and submit code and documentation patches of your own.
+
+Design Documents
+****************
+
+Read about ACRN's high-level design and architecture principles that led
+to the develoment of the ACRN hypervisor and its components.  You'll
+also find details about specific architecture topics.
+
+.. toctree::
+   :maxdepth: 1
+
+   developer-guides/modularity
+   developer-guides/hld/index
+   developer-guides/sw_design_guidelines
+   developer-guides/GVT-g-porting
+   developer-guides/trusty
+   developer-guides/l1tf
+   developer-guides/VBSK-analysis
+
+
+Contributing Documents
+**********************
+
+As an open-source project, we welcome and encourage the community to
+submit patches for code, documentation, tests, and more, directly to the
+project. Here's where you'll find how the development team works and the
+guidelines they (and you) use to contribute code (and documentation) to
+the project.
+
+.. toctree::
+   :maxdepth: 1
+
+   developer-guides/contribute_guidelines
+   developer-guides/coding_guidelines
+   developer-guides/doc_guidelines
+   developer-guides/graphviz
+   tutorials/docbuild