upd readme, license

CONTRIBUTING.md

@@ -1,3 +1,22 @@
+ ----
+
+Dear contributor,
+
+The repository you are contributing code to is also available with a different license on xs:code.
+
+I am using xs:code to offer paid access to a permissive licensed version of the code.
+
+In order to accept your contribution to this GPL licensed version, and to be able to use the contribution on the MIT licensed version as well, 
+I ask that you sign this CLA (Contributor license agreement) and send it to [email protected].
+
+Download the CLA here: https://github.com/olton/Metro-UI-CSS/blob/master/CLA.docx
+
+Without signing the CLA, I will not be able to accept your contribution.
+
+Thank you for your contribution and for your cooperation.
+
+ ----
+
 ## Issues Guidelines
 
 Before create issue: