add CONTRIBUTING and other documents

[antond-weta]

add
CONTRIBUTING.md
SECURITY.md
CODE_OF_CONDUCT.md
PULL_REQUEST_TEMPLATE.md

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.27%. Comparing base (4f1a2ce) to head (9d581b1).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #199   +/-   ##
=======================================
  Coverage   72.27%   72.27%           
=======================================
  Files          10       10           
  Lines        2348     2348           
  Branches      311      311           
=======================================
  Hits         1697     1697           
  Misses        651      651           

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