Make repos git cloneable by remote clients

[robocoder]

1. Add a configureable satis url in medusa.json as an alternative to absolute path file:// uris, e.g.,

    "satisurl": "http://user:password@satis.host:port/repo-home",

1. Update the readme to suggest co-locating the repositories folder inside the web folder.
2. Update medusa to automatically run git update-server-info inside each .git folder.