Mac M1 setup does not work without correct flags due to fastecdsa dependency

[D-DePablos]

Hi! This has been discussed in the nile GH, it might be good to state that a command which adequately uses gmp and clang assuming gmp is installed via brew and clang through pip is:

CFLAGS=-I`brew --prefix gmp`/include LDFLAGS=-L`brew --prefix gmp`/lib pip install ecdsa fastecdsa sympy

Because otherwise the error is rather non-descriptive.