The bare minimum to build PSP homebrews.
docker run --rm -it -v $(pwd):/source greatwizard/devkitpspdevkitPro is installed in /opt/devkitPro with examples for the PSP in the devkitPSP/psp/sdk/samples directory.
You can find several folders to demonstrate how to use various capabilities of the PSP.
To build an example, cd into its directory and run make.