This needs to go into the local tex distribution. On macos, this should be:
/usr/local/texlive/texmf-local/tex/latex
On linux, good luck. It should be in the home directory.
As of April 2022, I added a makefile to automate installing homework-math.cls
into the appropriate directories. This is custom to my set-up. If anyone sees
this repository, note that the makefile should be edited appropriately.