Adds youtubeDL-Material (#372)

* Adds YoutubeDL-Material with some suggestions from @Ornias1993

* test with 1000 user

* change to /data

* change tests to 568 and update docs

* doc update

docs/apps/stable/youtubedl-material/CONFIG.md

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+# Configuration Options
+
+##### Connecting to other apps
+If you need to connect this App to other Apps on TrueNAS SCALE, please refer to our "Linking Apps Together" guide:
+https://truecharts.org/manual/linking/
+
+##### Available config options
+In the future this page is going to contain an automated list of options available in the installation/edit UI.

docs/apps/stable/youtubedl-material/notes.md

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+# Installation Notes
+
+## By default Youtube-dl uses the following directories, which are NOT persistence. 
+## Everything in `/data`, `/app` and `/config` gets WIPED on boot.
+
+
+* Videos with 'Audio only' checked, by default downloads to `/data/audio/`
+* Video files, by default downlods to `/data/video`
+* Subscriptions ("watched" channels or playlists) by default downloads to `/data/subscriptions/`
+* If Multi-user is enabled all downloads goes, by default to `/data/users/` ignoring the previous mentioned directories
+
+To easily access the above directories, add them as custom storage. eg `/audio`, `/video`, `subscriptions`, `/users`  
+If you plan to use multi-user, you only need 1 directory, `/users`.
+DO NOT add custom storage in `/data`, `/app` and `/config` it will be wiped on the next boot.
+Then you have to manually map them on the WebUI also. (Top right corner > 3-Dots > Settings > Main and Downloader tabs)