[JENKINS-13423] Environment Variables documentation missing GIT_COMMIT and GIT_BRANCH

[dserodio]

This commit adds documentation for these, copied from the Jenkins Wiki but with "Gitish" replaced with "SHA-1 hash".

[orrc]

Probably this information doesn't belong in the core documentation, because the Git Plugin isn't part of core.

[dserodio]

I agree it's not part of core, but this is documented in the Jenkins "core" wiki. I think the static doc. included in Jenkins should have the same variables as the Wiki page I linked above.

Also, Git is very popular so I think this would be helpful for many people.

[dserodio]

PS.: Nice avatar :)

[orrc]

Well, the wiki is a wiki -- someone passing by just happened to add that info a few months ago.

I wonder if the list of available environment variables can somehow be dynamically generated, similar to some plugins which interact with the token-macro plugin do.

[kohsuke]

I hesitated a bit to comment without first changing my avatar, but anyway, I agree with orrc that the list should be dynamically generated.

[kohsuke]

I pushed pull-434.2 that contains just the contract part of it.

[kohsuke]

This change is merged toward 1.471. See jenkinsci/subversion-plugin@8ca12ea for an example of how to contribute environment variables to the help page from plugins

[dserodio]

Great! May I implement the environment variables contribution for the Git plugin?