Create post-update-hook

If the option "add_update_server_hook" is set during creation, git-update-server-info is added as hook. This allows instant use of the repo for anonymous access via webserver.
Add the new attribute to the readme
fix code-markup
Fix typo.
fix another typo
Merge pull request #1 from bcs-de/add_update_server_hook

Add update server hook