Since McOsu needs you to use an nsp anyways, I decided to make life easier and create a quick forwarder for it using Nro2Nsp. This will load from /switch/McOsu/McEngine.nro. There are two nsp's here. One has the normal McOsu logo, and one has the default osu logo. Install whichever one you choose.
Note: I did not create McOsu, go thank McKay42 for their amazing work! You can download the homebrew here: https://github.com/McKay42/McOsu-NX/releases