Compatiblity information for the docs

Added compatibility info under the Setting up section of the docs. 
Hi #dcarrot2!  I would say that it is only "compatible", not "compatibility".  Can you make that change?  Also, I'd say it is compatible "up to 2.7" although I'm not entirely sure of how best to phrase that.

If you make those changes, I would love to merge this.  :)