[PSCore Align] Update contributing docs with top-level CONTRIBUTING.md

[TylerLeonhardt]

To align with PowerShell Core's dev process/repo management.

[rkeithhill]

Is the plan to move this to a top-level CONTRIBUTING.md file? Maybe we need both? A top-level contributing guide (coding style, how to PR, expectations for a PR, etc) and a docs\development detailed guide on how to build the extension?

[TylerLeonhardt]

@rkeithhill Yeah what you're describing is exactly what we want.

I like the idea of a CONTRIBUTING.md being the top-level contributing guide (coding style, how to PR, expectations for a PR, etc) and then that can link to how to build and test the extension.

[TravisEz13]

We should also have a link to the microsoft code of conduct like in the PowerShell repo in the README.md:

## [Code of Conduct][conduct-md]

This project has adopted the [Microsoft Open Source Code of Conduct][conduct-code].
For more information see the [Code of Conduct FAQ][conduct-FAQ] or contact [opencode@microsoft.com][conduct-email] with any additional questions or comments.

[conduct-code]: http://opensource.microsoft.com/codeofconduct/
[conduct-FAQ]: http://opensource.microsoft.com/codeofconduct/faq/
[conduct-email]: mailto:opencode@microsoft.com
[conduct-md]: https://github.com/PowerShell/PowerShell/tree/master/./CODE_OF_CONDUCT.md

[Benny1007]

I think coding style, and conduct for me would be secondary to how the solution hangs together, implementing a basic feature by example, what tests are run and from where (dotnet test or full visual studio) and actually building and debugging the project.