If you want to actually implement an ACME client from first principles, reading the RFC (plus related RFCs for JOSE etc) is probably easier than you think. I did exactly that when I made a client for myself.

I also wrote up a digested description of the issuance flow here: https://www.arnavion.dev/blog/2019-06-01-how-does-acme-v2-wo... It's not a replacement for reading the RFCs, but it presents the information in the sequence that you would follow for issuance, so think of it like an index to the RFC sections.