[DOC] Clients OSC-dot-net

[landon-lengyel]

What do you want to do?

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request.
The documentation is lacking mention of how to actually authenticate with OpenSearch using this DotNet client.

*Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.
all

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
I am working on testing it now. I should be able to submit a PR shortly, but I am new to C# so it's slow going.