"Multi-variant playlist", not "variant stream"

Hi,

Just a point of detail (and not critical) but I believe that the section https://github.com/globocom/m3u8?tab=readme-ov-file#variant-playlists-variable-bitrates is not technically correct. The "main" playlist is called multi-variant, not variant stream (see https://datatracker.ietf.org/doc/html/draft-pantos-hls-rfc8216bis-14#section-4.4.6.2).

It seems to me therefore that the property should ideally be called `.is_multi_variant`

This would however be a breaking change, and may annoy a lot of people. Maybe just adding something to the documentation to avoid confusion with the spec?

Review the README section linked in the issue, “Variant Playlists (Variable Bitrates),” against the referenced HLS specification section. Clarify the terminology and explain the existing property without introducing an undocumented breaking change; the work is done when the README no longer conflates “multi-variant playlist” with “variant stream.”

Written by the indexing model from the issue text.