Docs refactor (#480)

Big docs refactor! Motivation is to make it easier for people to find
resources they are looking for. To accomplish this, there are now three
main sections:

- Getting Started: steps for getting started, walking through most core
functionality
- Modules: these are different modules of functionality that langchain
provides. Each part here has a "getting started", "how to", "key
concepts" and "reference" section (except in a few select cases where it
didnt easily fit).
- Use Cases: this is to separate use cases (like summarization, question
answering, evaluation, etc) from the modules, and provide a different
entry point to the code base.

There is also a full reference section, as well as extra resources
(glossary, gallery, etc)

Co-authored-by: Shreya Rajpal <ShreyaR@users.noreply.github.com>

docs/reference/prompts.rst

@@ -1,7 +1,7 @@
-LLMs & Prompts
+Prompts
 ==============
 
-The reference guides here all relate to objects for working with LLMs and Prompts.
+The reference guides here all relate to objects for working with Prompts.
 
 .. toctree::
    :maxdepth: 1
@@ -9,4 +9,3 @@ The reference guides here all relate to objects for working with LLMs and Prompt
 
    modules/prompt
    modules/example_selector
-   modules/llms