Tuist installation instructions need updating

[paul-brenner]

Following the Tuist installation steps in the readme gives an error that points to the new installation method:
https://docs.tuist.io/documentation/tuist/installation/

Which, on the one hand is fine because its pretty straightforward to just go to that link, install Mise, then install Tuist that way.

On the otherhand, as someone evaluating Sendbird as a solution for my company, it adds to the unsettling feeling that sendbird has been abandoned (or may be soon?).