SqlServerDsc: Add a CODE_OF_CONDUCT.md

[johlju]

Details of the scenario you tried and the problem that is occurring:
The recommended community standards suggest that we add a CODE_OF_CONDUCT.md file in the root of the repository. See https://github.com/PowerShell/SqlServerDsc/community.

I suggest we add a CODE_OF_CONDUCT.md with the same information as in the README.md. We can then raise an issue in DscResources asking if it is okay to remove the information from the README.md in favor of the CODE_OF_CONDUCT.md. Or, in the README.md point to the CODE_OF_CONDUCT.md.

The DSC configuration that is using the resource (as detailed as possible):
n/a

Version of the Operating System, SQL Server and PowerShell the DSC Target Node is running:
n/a

What module (SqlServer or SQLPS) and which version of the module the DSC Target Node is running:
n/a

Version of the DSC module you're using, or 'dev' if you're using current dev branch:
Dev