docs(README): move to .rst extension

MANIFEST.in

 include setup.py
-include README
+include README.rst
 
 recursive-include cubicweb_rqlcontroller *
 recursive-include cubicweb_rqlcontroller/data *.gif *.png *.ico *.css *.js

setup.py

@@ -45,7 +45,7 @@ author = __pkginfo__['author']
 author_email = __pkginfo__['author_email']
 classifiers = __pkginfo__['classifiers']
 
-with open(join(here, 'README')) as f:
+with open(join(here, 'README.rst')) as f:
     long_description = f.read()
 
 # get optional metadatas