[DOC] Update README with commit committer/author changes

Author: achambers

README.md

@@ -13,6 +13,11 @@ info.branch         //=> will be the current branch
 info.sha            //=> will be the current sha
 info.abbreviatedSha //=> will be the first 10 chars of the current sha
 info.tag            //=> will be the tag for the current sha (or `null` if no tag exists)
+info.committer      //=> will be the committer for the current sha
+info.committerDate  //=> will be the commit date for the current sha
+info.author         //=> will be the author for the current sha
+info.authorDate     //=> will be the authored date for the current sha
+info.commitMessage  //=> will be the commit message for the current sha
 ```
 
 When called without any arguments, `git-repo-info` will automatically lookup upwards