Update license in README

[robskillington]

No description provided.

[codecov]

Codecov Report

Merging #172 into master will decrease coverage by 0.34%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #172      +/-   ##
==========================================
- Coverage   78.14%   77.79%   -0.35%     
==========================================
  Files          83       83              
  Lines        3432     3432              
==========================================
- Hits         2682     2670      -12     
- Misses        682      694      +12     
  Partials       68       68

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