Improve osg-release.sh to show more errors
osg-release.sh should be made more user-friendly.
1- adding a usage message and
h being more explicit in communicating failures: e.g. if the tag/branch does not exist, the script outputs "error: pathspec 'v_yourbranch' did not match any file(s) known to git." but then continues and uploads an empty file to the OSG build host. Instead, it should print an error and stop