docs(README.md): add DeepWiki badge to project documentation

[NoSugarCoffee]

Add the DeepWiki badge to automatically update the wiki and facilitate a better understanding of the project.

What is DeepWiki?

DeepWiki provides up-to-date documentation you can talk to, for every repo in the world. Add this badge to your repository to help users find documentation.

[CLAassistant]

All committers have signed the CLA.

[svarlamov]

Thank you so much for the contribution @NoSugarCoffee! I appreciate the intention, but I reviewed the docs output and it doesn't quite match the quality and correctness that we aim to provide the Git AI ecosystem with. I'm going to close this PR for now, but please do check out the good first issue label in our issues list: https://github.com/acunniffe/git-ai/issues?q=is%3Aissue%20state%3Aopen%20label%3A%22good%20first%20issue%22

There's a lot of opportunities to contribute to Git AI and would love to catch up about how you're using Git AI and if there's anything we can help with: https://calendly.com/acunniffe/meeting-with-git-ai-authors