Refresh cheatsheet for OPA org

This PR makes a number of minor adjustments to how the cheatsheet is
rendered to return it to a two page doc after creeping up to 3 pages.

I have also made some updates to remove more styra references in the
content.

Signed-off-by: Charlie Egan <[email protected]>

Author: charlieegan3

SECURITY.md

@@ -0,0 +1,5 @@
+# Security Policy
+
+Please refer to the [OPA Security Policy](https://openpolicyagent.org/security)
+for details on how to report security issues, our disclosure policy, and how to
+receive notifications about security issues.