Documentation for .NET client is missing a backtick

[MichaelDeutschCoding]

docs/stack/get-started/om-clients/stack-dotnet.md is missing a backtick, causing the entire paragraph to appear monospaced like a code snippet.

I opened a PR #194 a few months ago, which seems to have fallen through the cracks. It's literally just one poor missing character 😟!

[dwdougherty]

Hi Michael. I'll see to it that your PR gets merged. I did add a comment to remove the double-quotes around REDIS_CONNECTION_STRING--they're superfluous. If you can commit that change, I'll approve the PR, etc.