Move back to a dev version and upgrade documentation

doc/whatsnew/2.10.rst

@@ -0,0 +1,18 @@
+***************************
+ What's New in Pylint 2.10
+***************************
+
+:Release: 2.10
+:Date: TBA
+
+Summary -- Release highlights
+=============================
+
+
+New checkers
+============
+
+
+
+Other Changes
+=============

doc/whatsnew/2.9.rst

@@ -3,11 +3,24 @@
 **************************
 
 :Release: 2.9
-:Date: TBA
+:Date: 2021-06-29
 
 Summary -- Release highlights
 =============================
 
+Pylint is now compatible with python 3.10.
+
+A lot of new checks have been added, some non-opinionated performance warnings
+like ``use-maxsplit-arg``, some consensual style warnings like
+``unnecessary-dict-index-lookup`` or new deprecation checks.
+
+We're aiming to reduce pylint noise for first time users and making some
+new checks optional is a step in that direction. In order to do that we
+created an optional code style checker that can be loaded using
+``pylint.extensions.code_style`` with the ``load-plugins`` options.
+More than ever, if as a veteran you want the most checks you can possibly get,
+[you should check the list of pylint extensions.](http://pylint.pycqa.org/en/latest/technical_reference/extensions.html#optional-pylint-checkers-in-the-extensions-module).
+
 
 New checkers
 ============

pylint/__pkginfo__.py

@@ -2,7 +2,7 @@
 # For details: https://github.com/PyCQA/pylint/blob/master/LICENSE
 from typing import Tuple
 
-__version__ = "2.9.0"
+__version__ = "2.9.1-dev0"
 
 
 def get_numversion_from_version(v: str) -> Tuple:

tbump.toml

@@ -1,7 +1,7 @@
 github_url = "https://github.com/PyCQA/pylint"
 
 [version]
-current = "2.9.0"
+current = "2.9.1-dev0"
 regex = '''
 ^(?P<major>0|[1-9]\d*)
 \.