Update README

[omarshaarawi]

Just a couple of suggestions to fix in the README.md.

1. In config.ts , the config file that is being looked at is ~/{HOME_DIR}/.commit-gpt.json. There isn't any mention of a config.json mentioned in the code base like it says in the README
2. The key that it's looking for is sessionKey not the snake case version session_key
3. Huge nitpick so ignore but your code runs git diff --cached which I just learned is no different than git diff --staged. However, maybe consider updating so it matches?

All nitpicks as I was having trouble getting this working without digging into the code to figure out what was expected.

For point 1 and 2, I know that if the config file doesn't exist, the it'll prompt to paste in the session key. This may be a separate issue but my terminals hung when trying to paste it in. I didn't want to create a separate issue yet until I confirmed it's not an issue I'm only experiencing.

[RomanHotsiy]

Thanks for the report! I'll take a look into it and get back to you.

[RomanHotsiy]

I updated the readme. Should be good now.

I copied a part about config.json from another project 🙈