Adding code of conduct definition

[shauheen]

This is the adopted code of conduct similar to CoreFX

[codecov]

Codecov Report

Merging #3449 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3449      +/-   ##
==========================================
+ Coverage   72.76%   72.76%   +<.01%     
==========================================
  Files         808      808              
  Lines      145452   145452              
  Branches    16244    16244              
==========================================
+ Hits       105836   105845       +9     
+ Misses      35195    35188       -7     
+ Partials     4421     4419       -2

Flag	Coverage Δ
#Debug	72.76% <ø> (ø)	⬆️
#production	68.28% <ø> (ø)	⬆️
#test	89.04% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
...ML.Transforms/Text/StopWordsRemovingTransformer.cs	86.1% <0%> (-0.16%)	⬇️
...crosoft.ML.Core/ComponentModel/ComponentCatalog.cs	67.95% <0%> (+0.17%)	⬆️
...soft.ML.Data/DataLoadSave/Text/TextLoaderCursor.cs	85.11% <0%> (+0.2%)	⬆️
...c/Microsoft.ML.FastTree/Utils/ThreadTaskManager.cs	100% <0%> (+20.51%)	⬆️

[shmoradims]

[eerhardt]

What's the difference/value in this over what is on the root README file?

https://github.com/dotnet/machinelearning#community