docs: update calendar and link releases notes for 20.1.4

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6034>
diff --git a/docs/relnotes.rst b/docs/relnotes.rst
index e96c4fb..38b405f 100644
--- a/docs/relnotes.rst
+++ b/docs/relnotes.rst
@@ -3,6 +3,7 @@
 
 The release notes summarize what's new or changed in each Mesa release.
 
+-  :doc:`20.1.4 release notes <relnotes/20.1.4>`
 -  :doc:`20.1.3 release notes <relnotes/20.1.3>`
 -  :doc:`20.1.2 release notes <relnotes/20.1.2>`
 -  :doc:`20.0.8 release notes <relnotes/20.0.8>`
@@ -309,6 +310,7 @@
    :maxdepth: 1
    :hidden:
 
+   relnotes/20.1.4
    relnotes/20.1.3
    relnotes/20.1.2
    relnotes/20.0.8