docs: how to contribute integrations (#28143)

docs/docs/contributing/how_to/code/guidelines.mdx

@@ -29,7 +29,7 @@ or new agents/chains from outside contributors without an existing GitHub discus
 
 - New features must come with docs, unit tests, and (if appropriate) integration tests.
 - New integrations must come with docs, unit tests, and (if appropriate) integration tests.
-  - See [this page](../integrations.mdx) for more details on contributing new integrations.
+  - See [this page](../integrations/index.mdx) for more details on contributing new integrations.
 - New functionality should not inherit from or use deprecated methods or classes.
 - We will reject features that are likely to lead to security vulnerabilities or reports.
 - Do not add any hard dependencies. Integrations may add optional dependencies.

docs/docs/contributing/how_to/index.mdx

@@ -2,4 +2,4 @@
 
 - [**Documentation**](documentation/index.mdx): Help improve our docs, including this one!
 - [**Code**](code/index.mdx): Help us write code, fix bugs, or improve our infrastructure.
-- [**Integrations**](integrations.mdx): Help us integrate with your favorite vendors and tools.
+- [**Integrations**](integrations/index.mdx): Help us integrate with your favorite vendors and tools.

docs/docs/contributing/how_to/integrations/community.mdx

@@ -0,0 +1,50 @@
+## How to add a community integration (deprecated)
+
+:::danger
+
+We are no longer accepting new community integrations. Please see the
+[main integration guide](./index.mdx) for more information on contributing new
+integrations.
+
+:::
+
+The `langchain-community` package is in `libs/community`.
+
+It can be installed with `pip install langchain-community`, and exported members can be imported with code like 
+
+```python
+from langchain_community.chat_models import ChatParrotLink
+from langchain_community.llms import ParrotLinkLLM
+from langchain_community.vectorstores import ParrotLinkVectorStore
+```
+
+The `community` package relies on manually-installed dependent packages, so you will see errors 
+if you try to import a package that is not installed. In our fake example, if you tried to import `ParrotLinkLLM` without installing `parrot-link-sdk`, you will see an `ImportError` telling you to install it when trying to use it.
+
+Let's say we wanted to implement a chat model for Parrot Link AI. We would create a new file in `libs/community/langchain_community/chat_models/parrot_link.py` with the following code:
+
+```python
+from langchain_core.language_models.chat_models import BaseChatModel
+
+class ChatParrotLink(BaseChatModel):
+    """ChatParrotLink chat model.
+
+    Example:
+        .. code-block:: python
+
+            from langchain_community.chat_models import ChatParrotLink
+
+            model = ChatParrotLink()
+    """
+
+    ...
+```
+
+And we would write tests in:
+
+- Unit tests: `libs/community/tests/unit_tests/chat_models/test_parrot_link.py`
+- Integration tests: `libs/community/tests/integration_tests/chat_models/test_parrot_link.py`
+
+And add documentation to:
+
+- `docs/docs/integrations/chat/parrot_link.ipynb`