Installation instructions for OS X not compatible with Apple Silicon

[njern]

Hello,

Recently built this for my M1 Macbook and realised the existing instructions only work for x86-based OS X computers.

I suggest updating the documentation.

Trying this out myself, when using Homebrew, it is easy to get it working by replacing the following line:

env ARCHFLAGS="-arch x86_64" LDFLAGS="-L/usr/local/opt/openssl/lib" CFLAGS="-I/usr/local/opt/openssl/include" pip install cryptography

With:

env ARCHFLAGS="-arch arm64" LDFLAGS="-L/opt/homebrew/opt/openssl@1.1/lib" CFLAGS="-I/opt/homebrew/opt/openssl@1.1/include" pip install cryptography

[jayjb]

Hi @njern,

Thanks! Ill give it a shot. If it works, maybe you could submit a PR?