docs(README): move to .rst extension

MANIFEST.in

 include *.py *.spec
 include */*.py
-recursive-include data *.gif *.png *.ico *.css *.js *.txt README
+recursive-include data *.gif *.png *.ico *.css *.js *.txt README.rst
 recursive-include i18n *.po
 recursive-include wdoc *

setup.py

@@ -57,7 +57,7 @@ author = pkginfo['author']
 author_email = pkginfo['author_email']
 classifiers = pkginfo['classifiers']
 
-with open(join(base_dir, 'README')) as f:
+with open(join(base_dir, 'README.rst')) as f:
     long_description = f.read()
 
 # get optional metadatas