I'm not sure keybase does this by default, but make sure to upload your key to a keyserver such as MIT's (https://pgp.mit.edu). Otherwise, git will complain that the signature is invalid when doing `git log --show-signature`.
Github doesn't complain for me, so I can only assume that it does this itself. What I did was grab my key from keybase and inserted that into my local keyring, then uploaded that to my github.
GitHub is happy as long as you upload the public key to GitHub. Git though uses pgp key servers to verify the signature.
This is only true if the person looking at the repo doesn't have a copy of your key locally. It's important to remember that all of these tools work offline and don't require some web 2.0 service to operate. :P