add SECURITY.md (#864)

* add SECURITY.md

Fixes: #699

* add Security mention to New issue template

* cleanup

.github/ISSUE_TEMPLATE/config.yml

@@ -11,3 +11,7 @@ contact_links:
   - name: 📱 Mobile Nebula
     url: https://github.com/definednet/mobile_nebula
     about: 'This issue tracker is not for mobile support. Try the Mobile Nebula repo instead!'
+
+  - name: 🔒 Report Security Vulnerability
+    url: https://github.com/slackhq/nebula/blob/master/SECURITY.md
+    about: 'Please view SECURITY.md to learn how to report security vulnerabilities.'

SECURITY.md

@@ -0,0 +1,12 @@
+Security Policy
+===============
+
+Reporting a Vulnerability
+-------------------------
+
+If you believe you have found a security vulnerability with Nebula, please let
+us know right away. We will investigate all reports and do our best to quickly
+fix valid issues.
+
+You can submit your report on [HackerOne](https://hackerone.com/slack) and our
+security team will respond as soon as possible.