Adds global.json

[SkyeHoefling]

Fixes: #28

Description

Adds docs for correct version of Visual Studio and .NET CLI. Adds global.json to force usage of .NET CLI 5.0.300+.

Merge Checklist

• Added unit or integration tests (if not explain)
• Benchmarks are equivalent or faster

[github-actions]

Benchmark Comparison

Benchmarking comparison between this Pull Request and the comitted values at benchmarks/results

thumbnail

 No differences found between the benchmark results with threshold 10%.
 

primary

 No differences found between the benchmark results with threshold 10%.
 

Benchmark Results

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BenchmarkDotNet=v0.13.0, OS=Windows 10.0.17763.2114 (1809/October2018Update/Redstone5)
Intel Xeon CPU E5-2673 v4 2.30GHz, 1 CPU, 2 logical and 2 physical cores
.NET SDK=5.0.400
 [Host]     : .NET 5.0.9 (5.0.921.35908), X64 RyuJIT
 Job-SGJCYN : .NET 5.0.9 (5.0.921.35908), X64 RyuJIT

Runtime=.NET 5.0  InvocationCount=1  LaunchCount=1  
UnrollFactor=1  

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated	Allocated native memory	Native memory leak
Thumbnail_Write	62.13 ms	1.236 ms	2.469 ms	-	-	-	280 B	5,125,137 B	-

primary

BenchmarkDotNet=v0.13.0, OS=Windows 10.0.17763.2114 (1809/October2018Update/Redstone5)
Intel Xeon CPU E5-2673 v4 2.30GHz, 1 CPU, 2 logical and 2 physical cores
.NET SDK=5.0.400
 [Host]     : .NET 5.0.9 (5.0.921.35908), X64 RyuJIT
 Job-WKYGQA : .NET 5.0.9 (5.0.921.35908), X64 RyuJIT

Runtime=.NET 5.0  InvocationCount=1  LaunchCount=1  
UnrollFactor=1  

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated	Allocated native memory	Native memory leak
PrimaryImage_Write	2.992 s	0.0248 s	0.0232 s	-	-	-	248 B	222,029,884 B	-