+Adds a "tag" reference in .git/refs/tags/
+
+Unless "-f" is given, the tag must not yet exist in ".git/refs/tags"
+
+If "-s" or "-a" is passed, the user will be prompted for a tag message.
+and a tag object is created. Otherwise just the SHA1 object
+name of the commit object is written.
+
+A GnuPG signed tag object will be created when "-s" is used.