update README

Author: ciur

README.md

@@ -30,3 +30,4 @@ repository.
 - Papermerge version 3.0.x docs are in git branch v3.0 # !
 - Papermerge version 3.1.x docs are in git branch v3.1 # !
 - Papermerge version 3.3 docs are in git branch v3.3
+- Papermerge version 3.5 docs are in git branch v3.5