DOCS: Update Turn/Matrix RTC sections for clarity

[MadMan247]

Hello,

The docs at https://matrix-construct.github.io/tuwunel/turn.html / https://matrix-construct.github.io/tuwunel/matrix_rtc.html are missing some points of clarity:

The TURN section states that it is required for calls. The Matrix RTC section does not, and instead assumes you're using docker compose. Since it's making an assumption, it would seem that it is optional, and only really matters if you're using docker.

What I can gather is the opposite; the Matrix RTC is required, but a dedicated TURN server is optional.

What I would like:

• Clarity for the requirements of calling
• what exactly does Matrix RTC do (e.g. explain that it is the main calling framework for modern matrix calls)
• Provide instructions for users NOT using Docker Compose
• If Matrix RTC is required, put it before the turn server in the docs.
• if TURN is required, either move the section for the built-in LiveKit turn server to the turn section, or emphasize in the turn section that instructions for the built-in turn server are in the Matrix RTC instructions.
• Mention what LiveKit is before it shows up in config files.