Starting some work on prebuilt_presets

src/ytdl_sub/prebuilt_presets/conventions.txt

@@ -0,0 +1,13 @@
+Prebuilt preset conventions:
+
+"Name Here"
+  - Should be 100% plug and play, and should represent the most common uses of ytdl-sub
+  - One version for each of the 3 supported players (Kodi, jellyfin, plex)
+  - For each of the main sources (youtube, soundcloud, bandcamp)
+
+name_here
+  - Should provide minor add-ons/adjustments to already working presets
+  - Can't be used stand-alone
+
+_name_here
+  - For behind the scenes presets that aren't expected to be in common use