add PMM Defaults changelog

PMM/CHANGELOG

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+# METADATA CHANGES
+Added Common Sense Selection [Movie](https://www.commonsensemedia.org/reviews/category/movie/tag/common-sense-selections-31822)] and [Show](https://www.commonsensemedia.org/reviews/category/tv/tag/common-sense-selections-31822) collections to `PMM/chart/other`
+Added several [visual styles for Separators](https://github.com/meisnate12/Plex-Meta-Manager-Images/tree/master/separators) to match PLEX's Categories theming. Called using `sep_style` template variable
+
+# OVERLAY CHANGES
+Added [Common Sense Age Rating](https://www.commonsensemedia.org/) overlays, called with `- git: PMM/overlays/age` and to be used in combination with operation `mass_content_rating_update: mdb_commonsense`
+Added Common Sense Selection overlays, called with `- git: PMM/overlays/commonsense_selection`
+Added [mediastinger](http://www.mediastinger.com/) overlays to indicate mid-credits and post-credits scenes, called with `- git: PMM/overlays/mediastinger`
+Added Oscars Ribbon overlay for [Best Picture Winners](https://www.imdb.com/search/title/?groups=best_picture_winner), called with `- git: PMM/overlays/oscars`