added git faq

docs/faq.md

@@ -1,6 +1,36 @@
 
 # Frequently asked questions
 
+## How does aider use git?
+
+It is recommended that you use aider with code that is part of a git repo.
+This allows aider to maintain the safety of your code. Using git makes it easy to:
+
+  - review the changes GPT made to your code
+  - undo changes that weren't appropriate
+  - manage GPT's changes on a git branch
+  - etc
+
+Working without git means that GPT might drastically change your code without an easy way to undo the changes.
+
+Aider tries to provide safety using git in a few ways:
+
+  - It asks to create a git repo if you launch it in a directory without one.
+  - Before sending requests to GPT, it checks if the repo is dirty and offers to commit those changes for you. This way, the GPT changes will be applied to a clean repo and won't be intermingled with your own changes.
+  - After GPT changes your code, aider commits those changes with a descriptive commit message.
+
+Aider also allows you to use in-chat commands to `/diff` or `/undo` the last change made by GPT.
+To do more complex management of your git history, you should use `git` on the command line outside of aider.
+You can start a branch before using aider to make a sequence of changes.
+Or you can `git reset` a longer series of aider changes that didn't pan out.
+
+While it is not recommended, you can disable aider's use of git in a few ways:
+
+  - `--no-auto-commits` will stop aider from git committing each of GPT's changes.
+  - `--no-dirty-commits` will stop aider from ensuring your repo is clean before sending requests to GPT.
+  - `--no-git` will completely stop aider from using git on your files. You should ensure you are keeping sensible backups of the files you're working with.
+
+
 ## GPT-4 vs GPT-3.5
 
 Aider supports all of OpenAI's chat models.