docs ecosystem/integrations update 3 (#5470)

# docs: `ecosystem_integrations` update 3

Next cycle of updating the `ecosystem/integrations`
* Added an integration `template` file
* Added missed integration files
* Fixed several document_loaders/notebooks

## Who can review?

Is it possible to assign somebody to review PRs on docs? Thanks.

docs/integrations/git.md

@@ -0,0 +1,19 @@
+# Git
+
+>[Git](https://en.wikipedia.org/wiki/Git) is a distributed version control system that tracks changes in any set of computer files, usually used for coordinating work among programmers collaboratively developing source code during software development.
+
+## Installation and Setup
+
+First, you need to install `GitPython` python package.
+
+```bash
+pip install GitPython
+```
+
+## Document Loader
+
+See a [usage example](../modules/indexes/document_loaders/examples/git.ipynb).
+
+```python
+from langchain.document_loaders import GitLoader
+```