Cherry pick security.txt

[jdorfman]

Lots of good ideas here:

• https://securitytxt.org/
• https://github.com/securitytxt/security-txt
• https://www.ietf.org/id/draft-foudil-securitytxt-00.txt

[jdorfman]

Cross promote

[jdorfman]

jsDelivr has a wiki page dedicated to the Bus Factor: https://github.com/jsdelivr/jsdelivr/wiki/What-to-do-if-I-die-aka-The-bus-factor

[jdorfman]

Another good article: https://daniel.haxx.se/blog/2017/08/02/the-curl-bus-factor/