Add note about nuget dev dependencies

[ericstj]

We mentioned dev dependencies in https://github.com/microsoft/component-detection/blob/main/docs/detectors/nuget.md#nugetprojectcentric but missed this other doc.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.9%. Comparing base (cd49c50) to head (be59d54).
⚠️ Report is 40 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1480     +/-   ##
=======================================
+ Coverage   89.6%   90.9%   +1.2%     
=======================================
  Files        402     423     +21     
  Lines      31734   37178   +5444     
  Branches    1959    2229    +270     
=======================================
+ Hits       28465   33813   +5348     
- Misses      2852    2922     +70     
- Partials     417     443     +26     

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