[1.6.x] Fixed #22924 -- Added a note about MEDIA_URL in templates.

Thanks raphael.herouart at gmail.com

Backport of 814bcc3395 from master
[1.6.x] Fixed various minor doc typos / references.

Backport of 67f9f385aa from master
[1.6.x] Fixed #22966 -- Clarified which release notes appear for each doc version.

Thanks haimunt at yahoo.com for the suggestion.

Backport of e6b3d6c22f from master
[1.6.x] Fixed #22942 -- Noted that __init__.py files are required for management command detection.

Thanks Diego Cerdán for the suggestion.

Backport of 54546cee88 from master