Add notes about community packages
Add notes about community packages

We now have a mix of official and non-official packages, make a note about trusting non-official ones.
gpbonillas/rust_for_rubyists,dskecse/rust_for_rubyists,dskecse/rust_for_rubyists,steveklabnik/rust_for_rubyists,gpbonillas/rust_for_rubyists,steveklabnik/rust_for_rubyists,steveklabnik/rust_for_rubyists,dskecse/rust_for_rubyists,gpbonillas/rust_for_rubyists