update README

[pedrolcl]

The documentation is a bit outdated.
For instance: document EAS_FM_SYNTH = ON by default, and also INSTALL_DEPENDENCIES.
Update workflows to avoid hardcoding the version number like in:

sonivox/.github/workflows/win-msvc.yml

Line 82 in d1bcc22

path: ${{github.workspace}}/build/sonivox-4.0.0-${{matrix.arch}}.exe

Producing this: