Add RELEASING.md

[andrewdavidmackenzie]

Fixes #349

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 32%. Comparing base (cc253b7) to head (11186bd).

Additional details and impacted files

@@          Coverage Diff          @@
##           master   #350   +/-   ##
=====================================
  Coverage      32%    32%           
=====================================
  Files          37     37           
  Lines        4340   4340           
=====================================
  Hits         1378   1378           
  Misses       2962   2962           

Flag	Coverage Δ
unittests	32% <ø> (ø)

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