I really, really recommend "The RISC-V Reader" by Patterson and Waterman. The book is really well written and gives a good understanding how RISC-V works as well as giving plenty examples of RISC-V assembly code (alongside ARM, x86 and MIPS).
If you want an introduction to low level computing in general, I'd recommend Computer Organization and Design: RISC-V Edition it uses RISC-V for all explanations and examples
The classic (plus an older, higher level book by the same authors)