Add a link to supported releases in the README and bug template

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1246>

.gitlab/issue_templates/Bug.md

@@ -8,7 +8,7 @@ first to ensure that you create a clear and specific issue.
 <!--
 Provide at least the following information:
 * Your OS and version
-* Affected GNOME Shell version
+* Affected GNOME Shell version (see https://wiki.gnome.org/Schedule for currently supported versions)
 * Does this issue appear in XOrg and/or Wayland
 -->