There are some information in obs_decam README and some partially outdated guide in
But they are incomplete and difficult for newcomers to follow.
DM-4624 should improve a lot, but some DECam-specific documentations would be helpful. (e.g. "we support both LSST and CP generated calibs; to use the one, do X, to use the other, do Y; limitations are..." suggested by John Swinbank in DM-5899)