Description of problem:
The User Guide does not cover how to create an application from a git URL.
From <rhc create-app --help>
--from-code URL URL to a Git repository that will become the initial contents of the application
Information can also be found on the Source Code bit on the Console when you create an application (the screen where you enter your app's name and indicate if it's scaling or not).
Could probably be in the Creating an Aplication section:
Note that there is also the table at the start of the topic that has the current options for <rhc create-app>. This will need to be added to this table too.
DOC UPDATE: Updated OpenShift Online User Guide with details on the above "--from code" option.