Merge #679: Add SECURITY.md

78c38363412db3ea1cd1f0cc42dd1624c078ee32 Add SECURITY.md (Jonas Nick)

Pull request description:

  Fixes #646

  WIP because the [email protected] email address doesn't exist yet. But it seems like the right place for vulnerability reports. [email protected] would have the downside that it perhaps reaches more people than necessary. Ideally secp256k1-security would just forward to the three maintainers listed in SECURITY.md. @sipa @apoelstra is it okay to put you there? Fwiw I'm opting out for now because three people should be enough.

  @sipa do you know who to talk to about adding [email protected] and the specifics about how it would work?

ACKs for top commit:
  real-or-random:
    ACK 78c38363412db3ea1cd1f0cc42dd1624c078ee32 I looked at the diff and verified my fingerprint

Tree-SHA512: 53a989615665cf8cf0c6a70d3bc2c4b71b68178cae40b2a7881aa9eba24732d126ba1e258a9fc127c69b47bb3025943097300cfcbbe18736cbf92ff4f3a901e0

diff --cc README.md
Simple merge