docs(csharp): update dotnet SDK README

[lukaszzborek]

• update readme to current state of .net SDK

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.41%. Comparing base (71eb4d5) to head (2c4774a).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2836      +/-   ##
============================================
+ Coverage     67.66%   68.41%   +0.74%     
+ Complexity      708      656      -52     
============================================
  Files          1030      850     -180     
  Lines         83846    67299   -16547     
  Branches      60704    58770    -1934     
============================================
- Hits          56733    46040   -10693     
+ Misses        24765    18925    -5840     
+ Partials       2348     2334      -14     

Flag	Coverage Δ
csharp	67.06% <ø> (-0.19%)	⬇️
go	?
node	?
python	?

Flags with carried forward coverage won't be shown. Click here to find out more.
see 237 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.