Show date in maintenance start timestamp

This will show "... as of 2014-03-27 14:29 CET."
Update README with better nginx/Apache examples

Update the README file with nginx and Apache configuration examples that’s compatible with unicorn, Passenger and other application servers, since many of them require you to use `current/public` as public web directory.
Merge pull request #17 from runar/update-readme

Update README with better nginx/Apache examples
Merge pull request #15 from twingly/date_to_timestamp

Show date in maintenance start timestamp