Resolve #106 + other small details

[mdrxy]

Fixes issue:

106

Proposed changes:

• Adds missing azuracast.env settings that have been added in recent versions
• Remove ADDITIONAL_MEDIA_SYNC_WORKER_COUNT as I couldn't find it used anymore in the project - looked to be outdated?
• I've seen it said that NOW_PLAYING_MAX_CONCURRENT_PROCESSES defaults to 5, however, I didn't see this reflected in the code - happy to change this if I missed something, but it looks like this default # will vary between installations
• Similarly, it is said that REDIS_HOST is set to redis for Docker installations, but it looks like it will always set to localhost - perhaps this was never updated either, or I am missing something.
• A myriad of small details / markdown syntax corrections / consistency enforcement across the entire docs aimed at resolving markdownlint issues + cleanliness

[mdrxy]

If ADDITIONAL_MEDIA_SYNC_WORKER_COUNT is indeed outdated, it should also be removed from the Dockerfile.