[Improvement] Display requirements in README

[liar666]

I could not manage to install company-tabnine for some time.

After discovering & trying the DoomEmacs Sandbox, and trying to install company-tabnine from there, I discovered an error message on a failing emacs-29.1 requirement.

So I finally understood that probably company-tabnine requires Emacs 29+, whereas I was using 28.1.

Would be great if these minimal requirements could be displayed somewhere, e.g. in the README page, so that people do not waste hours trying to find out why company-tabnine is not installing on their machine.

Thanks in advance