[FR] Better error message when using pnpm i -g

[wenfangdu]

After I changed my global npm registry, running pnpm i -g pkg throws

This modules directory was created using the following registries configuration: {"default":"https://registry.npmjs.org/"}. The current configuration is {"default":"http://registry.npm.foo.com/"}. To recreate the modules directory using the new settings, run "pnpm install".

I tried pnpm install multiple times with no success because, in fact, it should be pnpm i -g, I suggest adding the -g in the error message if the user was using pnpm i -g pkg, and don't add it if not.