installation page updated

[coleea]

hello.

First, this is my first PR ever. So some procedural error might exist.

I use M1 mac mini. Yesterday I tried to install rescript using npm i -g rescript. but failed because of errors.

I searched for internet and I found many people failed to install rescript on M1 mac device.

As I know, the best solution for this is downgrading npm version to 6.14. It seems like that npm version 8.x triggers installation error.

My conclusion is that the installation guide page https://rescript-lang.org/docs/manual/latest/installation need to be updated about M1 installation fail scenarios and solutions such as installing [email protected]. If not, many users even not try to rescript at all.