Add Documentation to Limit Repositories Displayed

[dradux]

I have a rather standard gitolite git system setup. After setting ginatra up and setting the git_dirs to my ~/repositories directory I found all repos were exposed. This can easily be changed/limted by creating a new directory and symlinking to the repos you want to expose.

For Example:

• git_root: ~/repositories
• public git repositories: ~/repos-public

In ~/repos-public:

• ln -s ../repositories/testing.git
  Now change the git_dirs config setting to use ~/repos-public and you will only see the testing.git repo.