Making getting started with omnigollum easier

I've added a Gollum configuration file which give an almost working example of how to setup a Gollum + Omnigollum wiki using LDAP and some other helpful options. I also updated the Readme to demonstrate how to use this config.rb file.

Other minor changes made include:
- Only showing the users nickname if the name does not exist. With omniauth-ldap name and nickname will [always be the same](https://github.com/intridea/omniauth-ldap/blob/master/lib/omniauth/strategies/ldap.rb).
- Added additional gems to the Gemfile including the version of mustache you specified in the Readme.md
- Updated the .gitignore file to match the default ruby ignore file provided by Github.