readme: add note about security related issues (#4401)
readme: add note about security related issues (#4401)

* readme: add note about security related issues

This is a reminder to encourage responsible disclosure (vs. publicly on GitHub) for security-related issues.

* readme: link to security page

kingland/consul,hashicorp/consul,calgaryscientific/consul,scalp42/consul,youhong316/consul,calgaryscientific/consul,hashicorp/consul,42wim/consul,youhong316/consul,kingland/consul,vamage/consul,scalp42/consul,scalp42/consul,hashicorp/consul,kingland/consul,hashicorp/consul,kingland/consul,vamage/consul,youhong316/consul,vamage/consul,youhong316/consul,42wim/consul,calgaryscientific/consul,42wim/consul,calgaryscientific/consul,scalp42/consul,42wim/consul,youhong316/consul,vamage/consul,vamage/consul,42wim/consul,kingland/consul,calgaryscientific/consul,scalp42/consul