docs(README): suggest the most reliable installation
docs(README): suggest the most reliable installation

There are different ways to install pnpm but the easiest
and most reliable option is to use npm. So a new user should
use the method that we are most confident about.

PR #2579
rstacruz/pnpm,rstacruz/pnpm,pnpm/pnpm,pnpm/pnpm,rstacruz/pnpm,pnpm/pnpm