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/lancedb.md

@@ -0,0 +1,23 @@
+# LanceDB
+
+This page covers how to use [LanceDB](https://github.com/lancedb/lancedb) within LangChain.
+It is broken into two parts: installation and setup, and then references to specific LanceDB wrappers.
+
+## Installation and Setup
+
+- Install the Python SDK with `pip install lancedb`
+
+## Wrappers
+
+### VectorStore
+
+There exists a wrapper around LanceDB databases, allowing you to use it as a vectorstore,
+whether for semantic search or example selection.
+
+To import this vectorstore:
+
+```python
+from langchain.vectorstores import LanceDB
+```
+
+For a more detailed walkthrough of the LanceDB wrapper, see [this notebook](../modules/indexes/vectorstores/examples/lancedb.ipynb)