Added note about compatibility with Node version

[danielbrauer]

Per #7 (comment)

[codecov-commenter]

Codecov Report

Merging #11 (fb4fa54) into master (913e754) will increase coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #11      +/-   ##
==========================================
+ Coverage   89.47%   89.58%   +0.11%     
==========================================
  Files          38       38              
  Lines        4255     4255              
  Branches      171      145      -26     
==========================================
+ Hits         3807     3812       +5     
  Misses        390      390              
+ Partials       58       53       -5     

Impacted Files	Coverage Δ
src/srp/SrpInteger.cs	96.20% <0.00%> (+0.63%)	⬆️
src/srp.tests/SrpAuthenticationTests.cs	59.82% <0.00%> (+0.85%)	⬆️
src/srp.tests/SrpIntegerTests.cs	99.50% <0.00%> (+1.47%)	⬆️

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[yallie]

Excellent, thank you very much! 🎉