Add CODE_OF_CONDUCT.md
Add CODE_OF_CONDUCT.md

Adds a standard Code of Conduct for Node.js repositories.

PR-URL: https://github.com/nodejs/email/pull/80
Reviewed-By: Rich Trott <28a7b6144c43947e3f532c033ff42c8a2ae08045@gmail.com>
Reviewed-By: Michael Dawson <241bf52ebd97cc4ec83d57b04d1f9e9053df032e@ca.ibm.com>

nodejs/email