docs: updates to `spack config get` docs for command-line scopes
docs: updates to `spack config get` docs for command-line scopes

iulian787/spack,LLNL/spack,iulian787/spack,iulian787/spack,iulian787/spack,mfherbst/spack,mfherbst/spack,LLNL/spack,krafczyk/spack,krafczyk/spack,iulian787/spack,LLNL/spack,mfherbst/spack,LLNL/spack,krafczyk/spack,krafczyk/spack,krafczyk/spack,LLNL/spack,mfherbst/spack,mfherbst/spack