Update the guide to reflect the issue with CLT Beta 3 and 4

[nezorflame]

Due to the issue with newer Command Line Tools for Xcode 15 beta (3 and 4 both have this issue), I've updated the guide stressing that you need the beta 2 version specifically.

Another update is regarding the xcode-select -p command output:

• if you have Xcode installed, then your guide is correct, but
• if you don't (and you don't need to have it in order to build the toolkit), then the output will be /Library/Developer/CommandLineTools instead of /Applications/Xcode-beta.app/Contents/Developer

[outcoldman]

I am going to close this PR. Just upgraded everything with Beta 6, and toolkit 1.03 - don't see any issues.