Readme update

[FoxClock]

Added detail to readme to assist MacOS users in configuring their machine to build the current state of the project.
Should alleviate the need for users to hunt down information on why their build is failing.

[FoxClock]

Seems that the CI runner is not resolving ${brew --prefix freetds}. This could be a linux issue or that the command is interpreted differently on this particular configuration.
It is confirmed working on my Intel Mac though. Problem is, we cant CI or ship my intel mac....

[vkuttyp]

Hi @FoxClock,

Thank you for this contribution! I have incorporated your documentation improvements and the PKG-Config troubleshooting guide
into the README.md.

I also updated ci/freetds.pc to include explicit instructions for both Apple Silicon and Intel Mac users. I opted to keep the
paths as static comments in the file rather than using the shell command ${brew --prefix} to ensure maximum compatibility with
standard pkg-config parsers, but the README now makes the configuration steps very clear.

This will be a huge help for other macOS users encountering linking issues. I've integrated these changes into the main branch.
Thanks again!