Article request for making your C9.io repo private.

[raisedadead]

Refer discussion on freeCodeCamp/freeCodeCamp#8854 and come up with a wiki article explaining steps to make a repo private on C9.

[raisedadead]

This may be referred and used in the challenges early on to guide users of risks and also in upcoming planed challenges in freeCodeCamp/freeCodeCamp#6669