update README

README.md

@@ -140,6 +140,8 @@ A release is made and uploaded to PyPI when a new tag is pushed to master branch
 
 ``cv_major.cv_minor.cv_revision.package_revision`` e.g. ``3.1.0.0``
 
+The master branch follows OpenCV master branch releases. 3.4 branch follows OpenCV 3.4 bugfix releases.
+
 ### Development builds
 
 Every commit to the master branch of this repo will be built. Possible build artifacts use local version identifiers:
@@ -166,4 +168,4 @@ Currently, builds for following Python versions are provided:
 - 3.5
 - 3.6
 - 3.7
-- 3.8
+- 3.8
\ No newline at end of file