Document quirk on Alpine Linux

[lukebakken]

I may be the only person to compile this project on Alpine, but I ran into this issue...

https://users.rust-lang.org/t/sigsegv-with-program-linked-against-openssl-in-an-alpine-container/52172

...when working on this PR - docker-library/rabbitmq#768

Perhaps build quirks should be documented somewhere?

[michaelklishin]

We can add a new file, e.g. BUILD.md, and explain that on distributions that load MUSL dynamically, such as Alpine, need to use a custom set of rustc args.