We're starting to get quite a lot of these ALL-CAPS.md documents.
There's been enough questions around how to properly use types like
EVP_MD_CTX that we probably should write down some of these common
rules.
Change-Id: I125f4e82efb168a071b54ff76c5af34c42ff4800
Reviewed-on: https://boringssl-review.googlesource.com/9115
Reviewed-by: Adam Langley <agl@google.com>
