Simplify and clarify env command usage?

[mkarajohn]

Currently the command to switch node version is pnpm env use --global <version>

In all pieces of documentation I could find, there is never another option other than --global passed to this command. There is also no mention of what happens if you omit this option either. Like, will the command fail? Will it do something that is not documented?

So, my suggestions are:

• First of all, if --global is mandatory and at the same time the only option, can the the command be simplified to just pnpm env use <version> ?
• If --global is not mandatory we should document what happens if it's omitted from the invocation
• If --global is not the only option we should document what are the other options and what do they do.

I'd be happy to update the docs