Document default of --location for pnpm config

[karlhorky]

Document the default of the --location flag for pnpm config commands

It appears that the default of the --location setting for pnpm config is global:

$ pnpm config set x true
$ pnpm config get x
true
$ cat "$HOME/Library/Preferences/pnpm/rc"
x=true

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[karlhorky]

Thanks for the review and merge!