Move doc files to extra-doc-files

README.md and CHANGELOG.md are not _source_ files.

Author: ffaf1

Cabal-hooks/Cabal-hooks.cabal

@@ -14,7 +14,7 @@ description:
 category:       Distribution
 build-type:     Simple
 
-extra-source-files:
+extra-doc-files:
   README.md CHANGELOG.md
 
 source-repository head