docs(README): move to .rst extension

MANIFEST.in

@@ -9,3 +9,4 @@ include test-requirements.txt
 prune __pkginfo__.py
 prune cubicweb-skos.spec
 prune debian
+include README.rst

setup.py

@@ -46,7 +46,7 @@ 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