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/ecosystem/nlpcloud.md

@@ -0,0 +1,17 @@
+# NLPCloud
+
+This page covers how to use the NLPCloud ecosystem within LangChain.
+It is broken into two parts: installation and setup, and then references to specific NLPCloud wrappers.
+
+## Installation and Setup
+- Install the Python SDK with `pip install nlpcloud`
+- Get an NLPCloud api key and set it as an environment variable (`NLPCLOUD_API_KEY`)
+
+## Wrappers
+
+### LLM
+
+There exists an NLPCloud LLM wrapper, which you can access with 
+```python
+from langchain.llms import NLPCloud
+```