New branching strategy

README.rst

@@ -6,6 +6,21 @@ ngtcp2
 ngtcp2 project is an effort to implement QUIC protocol which is now
 being discussed in IETF QUICWG for its standardization.
 
+Branching strategy
+------------------
+
+As of the beginning of draft-23 development, the new branching
+strategy has been introduced.  The master branch tracks the latest
+QUIC draft development.  When new draft-*NN* is published, the new
+branch named draft-*NN-1* is created based on the master branch.
+Those draft-*NN* branches are considered as "archived", which means
+that no update is expected.  PR should be made to the master branch
+only.
+
+For older draft implementations:
+
+- [draft-22](https://github.com/ngtcp2/ngtcp2/tree/draft-22)
+
 Requirements
 ------------