docs: compound ecosystem and integrations (#4870)

# Docs: compound ecosystem and integrations

**Problem statement:** We have a big overlap between the
References/Integrations and Ecosystem/LongChain Ecosystem pages. It
confuses users. It creates a situation when new integration is added
only on one of these pages, which creates even more confusion.
- removed References/Integrations page (but move all its information
into the individual integration pages - in the next PR).
- renamed Ecosystem/LongChain Ecosystem into Integrations/Integrations.
I like the Ecosystem term. It is more generic and semantically richer
than the Integration term. But it mentally overloads users. The
`integration` term is more concrete.
UPDATE: after discussion, the Ecosystem is the term.
Ecosystem/Integrations is the page (in place of Ecosystem/LongChain
Ecosystem).

As a result, a user gets a single place to start with the individual
integration.

docs/integrations/unstructured.md

@@ -0,0 +1,58 @@
+# Unstructured
+
+This page covers how to use the [`unstructured`](https://github.com/Unstructured-IO/unstructured)
+ecosystem within LangChain. The `unstructured` package from
+[Unstructured.IO](https://www.unstructured.io/) extracts clean text from raw source documents like
+PDFs and Word documents.
+
+
+This page is broken into two parts: installation and setup, and then references to specific
+`unstructured` wrappers.
+
+## Installation and Setup
+
+If you are using a loader that runs locally, use the following steps to get `unstructured` and
+its dependencies running locally.
+
+- Install the Python SDK with `pip install "unstructured[local-inference]"`
+- Install the following system dependencies if they are not already available on your system.
+  Depending on what document types you're parsing, you may not need all of these.
+    - `libmagic-dev` (filetype detection)
+    - `poppler-utils` (images and PDFs)
+    - `tesseract-ocr`(images and PDFs)
+    - `libreoffice` (MS Office docs)
+    - `pandoc` (EPUBs)
+- If you are parsing PDFs using the `"hi_res"` strategy, run the following to install the `detectron2` model, which
+  `unstructured` uses for layout detection:
+    - `pip install "detectron2@git+https://github.com/facebookresearch/detectron2.git@e2ce8dc#egg=detectron2"`
+    - If `detectron2` is not installed, `unstructured` will fallback to processing PDFs
+      using the `"fast"` strategy, which uses `pdfminer` directly and doesn't require
+      `detectron2`.
+
+If you want to get up and running with less set up, you can
+simply run `pip install unstructured` and use `UnstructuredAPIFileLoader` or
+`UnstructuredAPIFileIOLoader`. That will process your document using the hosted Unstructured API.
+Note that currently (as of 1 May 2023) the Unstructured API is open, but it will soon require
+an API. The [Unstructured documentation page](https://unstructured-io.github.io/) will have
+instructions on how to generate an API key once they're available. Check out the instructions
+[here](https://github.com/Unstructured-IO/unstructured-api#dizzy-instructions-for-using-the-docker-image)
+if you'd like to self-host the Unstructured API or run it locally.
+
+## Wrappers
+
+### Data Loaders
+
+The primary `unstructured` wrappers within `langchain` are data loaders. The following
+shows how to use the most basic unstructured data loader. There are other file-specific
+data loaders available in the `langchain.document_loaders` module.
+
+```python
+from langchain.document_loaders import UnstructuredFileLoader
+
+loader = UnstructuredFileLoader("state_of_the_union.txt")
+loader.load()
+```
+
+If you instantiate the loader with `UnstructuredFileLoader(mode="elements")`, the loader
+will track additional metadata like the page number and text type (i.e. title, narrative text)
+when that information is available.