docs/release-calender: Add 20.2 stable releases

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6904>
diff --git a/docs/release-calendar.rst b/docs/release-calendar.rst
index 6ee2c6a..51dc403 100644
--- a/docs/release-calendar.rst
+++ b/docs/release-calendar.rst
@@ -32,3 +32,11 @@
 +========+===============+============+=================+=========================================+
 | 20.1   | 2020-10-14    | 20.1.10    | Eric Engestrom  | Last planned release of the 20.1 series |
 +--------+---------------+------------+-----------------+-----------------------------------------+
+| 20.2   | 2020-10-14    | 20.2.1     | Dylan Baker     |                                         |
++--------+---------------+------------+-----------------+-----------------------------------------+
+| 20.2   | 2020-10-28    | 20.2.2     | Dylan Baker     |                                         |
++--------+---------------+------------+-----------------+-----------------------------------------+
+| 20.2   | 2020-11-11    | 20.2.3     | Dylan Baker     |                                         |
++--------+---------------+------------+-----------------+-----------------------------------------+
+| 20.2   | 2020-11-24    | 20.2.4     | Dylan Baker     |                                         |
++--------+---------------+------------+-----------------+-----------------------------------------+