Add NuGet README file

[luisquintanilla]

We are excited to review your PR.

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• There's a descriptive title that will make sense to other developers some time from now.
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Fixes #5899

[michaelgsharp]

Sorry, been OOF but I'm back now. Path needs fixing, but otherwise I think its good.

[michaelgsharp]

I'm thinking that maybe its getting stuck on the symbols package. I was able to get the readme in the normal package just fine, but it just fails when it tries to do the symbols one.

[chrisraygill]

@luisquintanilla What version of the .NET SDK are you using to pack? We had an issue that didn't allow README inclusion when using snupkg for symbols, but it was fixed in .NET 6 RC 2.

[luisquintanilla]

@chgill-MSFT I believe ML.NET targets .NET Standard 2.0. @michaelgsharp would know better though.

[michaelgsharp]

The PR that updated us to use the fixed version of .NET 6 just went in yesterday. I have fixed the include to point to the right readme file and this now works as expected. Once the builds pass I can merge this in.

[michaelgsharp]

LGTM.

[codecov]

Codecov Report

Merging #5900 (39ae7dc) into main (526215d) will increase coverage by 0.39%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #5900      +/-   ##
==========================================
+ Coverage   68.19%   68.58%   +0.39%     
==========================================
  Files        1142     1146       +4     
  Lines      242367   245395    +3028     
  Branches    25355    25634     +279     
==========================================
+ Hits       165273   168314    +3041     
+ Misses      70409    70385      -24     
- Partials     6685     6696      +11     

Flag	Coverage Δ
Debug	68.58% <ø> (+0.39%)	⬆️
production	63.38% <ø> (+0.51%)	⬆️
test	88.67% <ø> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...c/Microsoft.ML.FastTree/Utils/ThreadTaskManager.cs	79.48% <0.00%> (-20.52%)	⬇️
...c/Microsoft.ML.Data/Prediction/PredictionEngine.cs	87.83% <0.00%> (-4.81%)	⬇️
src/Microsoft.ML.TimeSeries/PredictionEngine.cs	76.96% <0.00%> (-3.63%)	⬇️
...ansforms/PermutationFeatureImportanceExtensions.cs	92.30% <0.00%> (-3.57%)	⬇️
src/Microsoft.ML.OnnxTransformer/OnnxUtils.cs	84.48% <0.00%> (-2.15%)	⬇️
.../Microsoft.ML.Data/Model/ModelOperationsCatalog.cs	53.60% <0.00%> (-1.78%)	⬇️
src/Microsoft.ML.Maml/MAML.cs	25.38% <0.00%> (-1.53%)	⬇️
src/Microsoft.Data.Analysis/Strings.Designer.cs	43.26% <0.00%> (-0.95%)	⬇️
src/Microsoft.ML.Data/DataView/CacheDataView.cs	83.96% <0.00%> (-0.68%)	⬇️
src/Microsoft.ML.Transforms/GroupTransform.cs	91.37% <0.00%> (-0.64%)	⬇️
... and 75 more