Don't add #commits to forks by default

[0xallie]

Forks imported from GitHub shouldn't be announced to #commits by default, because that can cause confusion between the upstream repository and the fork.

Perhaps there should be a warning suggesting not to add your fork to a generic commits channel such as #commits unless you use the full project name.

See also

• Issue #62

[TkTech]

We should be able to do this. The Github API returns fork information (as long as the original project still exists) when we import.