--playlist--start and --playlist-end more verbosity suggestion

[burtek]

Checklist

• I'm reporting a feature request
• I've verified that I'm running youtube-dl version 2019.11.28
• I've searched the bugtracker for similar feature requests including closed ones

Description

While using youtube-dl <playlisit-id> --playlist-start 10 on a playlist containing 60 videos, youtube-dl displays 50 videos in playlist and counts them from 1 to 50 (Downloading video 1 od 50). When user does not know the exact count of videos in playlist, they don't know if --playlist-start works or not. There is no indication of that whatsoever.

My idea is to show more verbose info when using --playlist--start and --playlist-end. Assuming one is running youtube-dl <playlisit-id> --playlist-start 10 --playlist-end 30 on a playlist mentioned earlier, the message could be as follows:

...
[youtube:playlist] playlist <playlist-name>: Downloading 20 out of 60 videos
[download] Downloading video 1 of 20 (playlist video 10)
...

This way the user gets two important pieces of information:

1. The --playlist--start and --playlist-end switches do work,
2. In case a download fails somewhere in the middle of the queue, the playlist video nn on [download] line tells exactly with what --playlist--start index should the download be re-started

I believe this change won't require much work, but the result would pretty big for users.