add missing introductory sentence

Author: TC-MO

sources/academy/platform/get_most_of_actors/actor_readme.md

@@ -5,6 +5,8 @@ sidebar_position: 2
 slug: /get-most-of-actors/actor-readme
 ---
 
+**Learn how to write a comprehensive README to help users better navigate, understand and run public Actors in Apify Store.**
+
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