Update security policy (#11374)

* Update security policy

I like this paragraph from the wagtail project https://docs.wagtail.org/en/latest/contributing/security.html#bug-bounties :)

* Tests: set privacy level to public explicitly

Fixes tests on .com

* Revert "Tests: set privacy level to public explicitly"

This reverts commit e00fce3.

docs/user/security.rst

@@ -55,6 +55,7 @@ Bug bounties
 
 While we sincerely appreciate and encourage reports of suspected security problems,
 please note that the Read the Docs is an open source project, and **does not run any bug bounty programs**.
+But we will gladly give credit to you and/or your organization for responsibly reporting security issues.
 
 Security issue archive
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