Specify the required version of Zig in the README

[ducdetronquito]

Hi @Vexu !

Would it be possible to specify the required version of Zig to work with zuri ? (v0.6.0 or master)
If it is the master branch, what are the reasons to use it over the last stable release ?

Have a nice day ! :)

[Veikka Tuominen]

Here you go: 8f5a0bf. Zig master version is used by default since that's what majority of Zig users use due to it being required by the language server.

[ducdetronquito]

Thank you :)