Add manual pipeline run variables to priority section

doc/ci/variables/README.md

@@ -492,7 +492,8 @@ variables, depending on where they are defined.
 
 The order of precedence for variables is (from highest to lowest):
 
-1. [Trigger variables](../triggers/README.md#making-use-of-trigger-variables) or [scheduled pipeline variables](../pipelines/schedules.md#using-variables).
+1. [Trigger variables](../triggers/README.md#making-use-of-trigger-variables), [scheduled pipeline variables](../pipelines/schedules.md#using-variables),
+   and [manual pipeline run variables](#override-a-variable-by-manually-running-a-pipeline).
 1. Project-level [variables](#custom-environment-variables) or [protected variables](#protect-a-custom-variable).
 1. Group-level [variables](#group-level-environment-variables) or [protected variables](#protect-a-custom-variable).
 1. [Inherited environment variables](#inherit-environment-variables).