docs: add release calendar page and references to it

Add a page that has information which release is expected when and
associated information.

Reference to it from the "Releasing process" and "Release notes" pages.

v2:
 - Add Andres for 17.0.5
 - Rework table format to include the branch (Eric)

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Andres Gomez <agomez@igalia.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
diff --git a/docs/releasing.html b/docs/releasing.html
index fc7f2a5..15df022 100644
--- a/docs/releasing.html
+++ b/docs/releasing.html
@@ -53,6 +53,9 @@
 <p>
 Releases should happen on Fridays. Delays can occur although those should be keep
 to a minimum.
+<br>
+See our <a href="release-calendar.html" target="_parent">calendar</a> for the
+date and other details for individual releases.
 </p>
 
 <h2>Feature releases</h2>