Add `git.describe` command

[IcanDivideBy0]

Add `git.describe` command

[IcanDivideBy0]

git.exec({
  args: 'describe --abbrev=0 --tags',
  quiet: true
}, (err, latestTag) => { ... });

[IcanDivideBy0]

Nevermind, git.exec is enouth for that!

[davidmaxwaterman]

I'd quite like to know how you made 'git.exec' work for this.

[stephenlacy]

Want to add it to the examples?

[IcanDivideBy0]

I think the log example is already enouth. This one won't add anything more relevant to the doc.