Document C# Coverlet Cobertura workaround

Problem to solve

Right now the C# documentation for the inline code coverage cobertura report parsing does not always work out of the box, due to how coverlet builds the cobertura reports. Full details: #213444 (comment 334104771)

Proposal

We should document the above workaround in the documentation so people are aware that their coverlet coverage reports may not work out of the box with the inline-code-coverage feature.

Who can address the issue

Anyone familiar with the inline-code-coverage feature, or anyone in grouptesting

Other links/references