Update .gitattributes

To further avoid useless merge conflicts.

Author: sbidoul

.gitattributes

@@ -1,5 +1,8 @@
 # ignore some autogenerated files when merging
 # git config --global merge.ours.driver true
+/README.md merge=ours
+/*/__manifest__.py merge=ours
 /*/i18n/* merge=ours
+/*/readme/HISTORY.rst merge=ours
 /*/README.rst merge=ours
 /*/static/description/index.html merge=ours