Added FAQ doc

FAQ.md

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+### Why can't I add a new show to Radarr, its on TMDb? ###
+
+Radarr uses themoviedb.org for movie information and for images (fanart, banners, images) and there are two reasons why you may not be able to add it:
+
+1. TMDb doesn't like special characters to be used when searching for series through the API (which Radarr uses), so try searching a translated name, and/or without special characters.
+2. The movie hasn't been added to TMDb yet, follow their guide to get it added: https://www.themoviedb.org/documentation/editing/movies