Merge #8786: Mandatory copyright agreement

4b67402 Mandatory copyright agreement (Andrew Chow)

Author: laanwj

CONTRIBUTING.md

@@ -198,3 +198,11 @@ Release Policy
 --------------
 
 The project leader is the release manager for each Bitcoin Core release.
+
+Copyright
+---------
+
+By contributing to this repository, you agree to license your work under the 
+MIT license unless specified otherwise in `contrib/debian/copyright` or at 
+the top of the file itself. Any work contributed where you are not the original 
+author must contain its license header with the original author(s) and source.