Add documentation for JSON/RSS formats

[denizdogan]

Originally reported here: Radarr/Radarr#8370

There's literally no documentation at all for custom JSON/RSS formats as far as I've been able to find.

[mynameisbogdan]

@denizdogan can you try these examples for me?

For Steven Lu:

[
    {
        "title": "Weird: The Al Yankovic Story",
        "imdb_id": "tt17076046"
    },
    {
        "title": "Ant-Man and the Wasp: Quantumania",
        "imdb_id": "tt10954600"
    },
    {
        "title": "Shin Ultraman",
        "imdb_id": "tt10737918"
    }
]

For Custom List with TMDB IDs:

[
    {
        "id": 928344
    },
    {
        "id": 640146
    },
    {
        "id": 634429
    }
]

[sjlu]

@mynameisbogdan I started adding tmdb_id to the list.

[bakerboy448]

8d7e8a8