According to Volume I: RISC-V Unprivileged ISA V20191213
Table 27.1: Standard ISA extension names. The table also defines the canonical order in which
extension names must appear in the name string, with top-to-bottom in table indicating first-to-last
in the name string, e.g., RV32IMACV is legal, whereas RV32IMAVC is not.
According to Volume I: RISC-V Unprivileged ISA V20191213
So, I modified the README accordingly.