Update readme to clarify the version for each PrestaShop version

Author: jolelievre

README.md

@@ -9,7 +9,9 @@ Branches on this repository follow PrestaShop Core branches
 
 - branch `2.0.x` follows development of PrestaShop `8.0.x` branch
 - branch `2.1.x` follows development of PrestaShop `8.1.x` branch
-- branch `develop` follows development of PrestaShop `develop` branch
+- branch `2.2.x` follows development of PrestaShop `8.2.x` branch
+- branch `3.0.x` follows development of PrestaShop `9.0.x` branch
+- branch `develop` for version `3.1` follows development of PrestaShop `9.1.x` branch
 
 That means changes in branch `2.1.x` branch will be delivered with PrestaShop 8.1.x versions.