Document prerequisites/requirements for Yocto builds

[tronical]

Certain features such as the LinuxKMS backend or the Skia renderer have certain system requirements on system libraries and tools. We should document how to satisfy these requirements while building Yocto images and SDKs.

[tronical]

See also #1234 as well as https://github.com/slint-ui/meta-slint#building-an-sdk-for-external-slint-builds