The wiki tutorial page (https://github.com/mongodb/mongo-ruby-driver/wiki/Tutorial) references an examples directory that doesn't exist (https://github.com/mongodb/mongo-ruby-driver/tree/master/examples).
I think this should have been When the examples were moved from the readme to the wiki (commit 6e96d52 I think). I removed the reference and have attached a diff if you're inclined to use it.