Create SECURITY.md

[squell]

This is a copy of the ntpd-rs policy ands links to the ntpd-rs repository; that keeps everything in one place.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.14%. Comparing base (6c8c448) to head (7d1c25a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #890      +/-   ##
==========================================
- Coverage   64.33%   64.14%   -0.20%     
==========================================
  Files          62       62              
  Lines        8093     8093              
==========================================
- Hits         5207     5191      -16     
- Misses       2886     2902      +16     

Flag	Coverage Δ
fuzz	15.96% <ø> (-0.88%)	⬇️
fuzz-message_sound	15.96% <ø> (-0.88%)	⬇️

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