Document hub config file format

[gibfahn]

It would be nice to document the hub config file format somewhere.

When I set this up I had to read through the hub source to work out what the config should look like, and was unable to get toml to work.

For example my current config looks like this:

github.com:
- user: <username>
  oauth_token: "<token>"
  protocol: https

# GHE
github.<myorg>.com:
- user: <username>
  oauth_token: "<token>"
  protocol: https

I'd be happy to raise a PR, but I'm not sure where the best place would be, maybe in the README? In man hub?

[mislav]

Thank you, but instead of documenting the config file format, I would rather that we create a command that will write out that config file for you. #225 I generally want to avoid training people to edit config files by hand.

[gibfahn]

That makes sense, but given that #225 is not far off its tenth anniversary and that gh is likely to become the main focus before it gets solved, a quick fix like including a sample config in the README would be really helpful.

Also there are always cases where it's annoying to have to use the command to edit the format, in which case having it documented is extremely helpful.