Added a document on contributing, with a link to a place to sign it, and also a copy of the text of the agreement.
Added a document on contributing, with a link to a place to sign it, and also a copy of the text of the agreement.

drewmccormack/ensembles,drewmccormack/ensembles,ChronicStim/ensembles,realmacsoftware/ensembles,ChronicStim/ensembles,realmacsoftware/ensembles