Refs #24115 -- Added docs for password updates on bcrypt rounds change.

docs/topics/auth/passwords.txt

@@ -191,8 +191,13 @@ can switch to new (and better) storage algorithms as they get invented.
 However, Django can only upgrade passwords that use algorithms mentioned in
 :setting:`PASSWORD_HASHERS`, so as you upgrade to new systems you should make
 sure never to *remove* entries from this list. If you do, users using
-unmentioned algorithms won't be able to upgrade. Passwords will be upgraded
-when changing the PBKDF2 iteration count.
+unmentioned algorithms won't be able to upgrade. Hashed passwords will be
+updated when increasing (or decreasing) the number of PBKDF2 iterations or
+bcrypt rounds.
+
+.. versionchanged:: 1.9
+
+    Passwords updates when changing the number of bcrypt rounds was added.
 
 .. _sha1: https://en.wikipedia.org/wiki/SHA1
 .. _pbkdf2: https://en.wikipedia.org/wiki/PBKDF2
@@ -200,7 +205,6 @@ when changing the PBKDF2 iteration count.
 .. _bcrypt: https://en.wikipedia.org/wiki/Bcrypt
 .. _`bcrypt library`: https://pypi.python.org/pypi/bcrypt/
 
-
 Manually managing a user's password
 ===================================