docs: Add the favicon to the new page.

Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4630>
diff --git a/docs/conf.py b/docs/conf.py
index 3ca6352..26beed3 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -95,6 +95,8 @@
 #
 html_theme = 'sphinx_rtd_theme'
 
+html_favicon = "favicon.ico"
+
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.