Download Meeting: Warn about /video mount permissions

[oxzi]

Is your feature request related to a problem? Please describe.
When recording a meeting with BBB_DOWNLOAD_MEETING=true resp. -d/--download, the /video mount must be writable for the container user.

By dropping permissions to the user with the UID 1001 within the Dockerfile, this user needs write permissions to save recordings. However, often the user's UID on the host differs from this UID, resulting in insufficient permissions and ffmpeg to fail.

As both docker-entrypoint.sh and startStream.sh are executed under UID 1001, one cannot chown/chmod at this point anymore. Thus, an easy but hackish solution is to chown 1001 videodata on the host before starting the container.

Describe the solution you'd like
I would like to see a comment within the documentation next to BBB_DOWNLOAD_MEETING indicating one should adjust the directory's ownership or permissions.

Describe alternatives you've considered
An even cleaner solution would be to run the ENTRYPOINT as root, change directory permissions if necessary and drop user permissions to UID 1001 within the script afterwards.

Additional context
None, I guess.