Update Conditions update Featured videos for main site.md

rules/Conditions update Featured videos for main site.md

@@ -16,6 +16,7 @@
 - The video must not be: Immoral, violent, sexual content, harmful or dangerous content, incitement to racial hatred, violent or dangerous content.
 
 - Videos are checked by 5 curators and give a subjective assessment, if one curator disagrees, the video will not be approved.
+- The video is updated once a month.
 
 `Annihilation
 The video violates any license or copyright (and does not fall under "fair use")`