Upgrade branches in GIT-RULES

Author: nikic

README.GIT-RULES

@@ -44,23 +44,24 @@ Having said that, here are the organizational rules::
 
 Currently we have the following branches in use::
 
-  master    The active development branch.
+  master    Active development branch for PHP 8.0, which is open for
+            backwards incompatible changes and major internal API changes.
+
+  PHP-7.4   Active development branch for PHP 7.4, which is open for
+            new features and minor internal API changes.
 
   PHP-7.3   Is used to release the PHP 7.3.x series. This is a current
-            non stable version and is open for bugfixes and minor improvements
-            only.
+            stable version and is open for bugfixes only.
 
   PHP-7.2   Is used to release the PHP 7.2.x series. This is a current
             stable version and is open for bugfixes only.
 
   PHP-7.1   Is used to release the PHP 7.1.x series. This is an old
             stable version and is open for security fixes only.
 
-  PHP-7.0   Is used to release the PHP 7.0.x series. This is an old
-            stable version and is open for security fixes only.
+  PHP-7.0   This branch is closed.
 
-  PHP-5.6   Is used to release the PHP 5.6.x series. This is an old
-            stable version and is open for security fixes only.
+  PHP-5.6   This branch is closed.
 
   PHP-5.5   This branch is closed.