Update CHANGELOG.rst (#638)

Co-authored-by: Humberto Diógenes <hdiogenes@gmail.com>

Author: cmagnobarbosa

CHANGELOG.rst

@@ -21,6 +21,24 @@ Fixed
 Security
 ========
 
+[2021.final-rc1] - "final" release candidate 1 - 2021-04-30
+***********************************************************
+
+Added
+=====
+- Added a string representation method to ``GroupMod``,
+  ``Header``, ``Bucket``, ``ActionSetField`` and ``ActionOutput``.
+
+Changed
+=======
+- Changed ``setup.py`` to run ``pytest-runner`` only during the unit tests.
+- Let Scrutinizer CI choose which Python 3.6 it'll use for tests.
+
+Fixed
+=====
+- Fixed ``PackException`` error when running Kytos with OpenFlow 1.0 (#631).
+- Fixed docstrings in ``UBIntBase`` and ``TableFeatures`` classes.
+
 
 [2020.2] - "itamar" stable release - 2020-12-30
 ***********************************************