[Instrumentation.Runtime] Add description for metrics in README.md

[xiang17]

Changes

Add description for metrics in README.md

For significant contributions please make sure you have completed the following items:

• Design discussion issue Bringing .NET Runtime metrics instrumentation to Stable #335

[codecov]

Codecov Report

Merging #475 (aa17f91) into main (361d704) will not change coverage.
The diff coverage is 0.00%.

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...elemetry.Instrumentation.Runtime/RuntimeMetrics.cs	0.00% <0.00%> (ø)

[cijothomas]

I'd suggest to use heading for each of the metric, instead of the table. It'll be easier to link to individual metric that way. And we can write very long, details about the metric. (Description in this doc is not that important, as it is already part of metric descripption.) We could do more here, like "what value is considered typically okay, what is the action item if this value is high/low etc."

[cijothomas]

eventually "tutorials:" like this : https://docs.microsoft.com/en-us/dotnet/core/diagnostics/debug-threadpool-starvation

[xiang17]

I was more of thinking to make it easier for people who want to have a quick glance to know what to expect without having to dive into the code. I like your tutorial idea, and we can also include tools to use, etc. but it would be much more than the scope of this PR.

[twenzel]

@xiang17 Looks good to me

[xiang17]

@xiang17 Looks good to me

Thanks!

[noahfalk]

LGTM!