Docs: Document System.Hashcode in .NET Core 2.1 API

[ChrisMaddock]

https://docs.microsoft.com/en-gb/dotnet/api/system.hashcode?view=netcore-2.1

New API which is currently undocumented.

[mairaw]

Thanks for filing this @ChrisMaddock.

Related notes: https://github.com/dotnet/corefx/issues/14354

@karelz do you know who owns this? And do you think it would be possible to get the dev team to help fill out the "To be added" segments here with some basic comments?

[karelz]

@morganbr was championing the change - he should be able to help / recommend others.

[morganbr]

I'm willing to help out. What do you need for this?

[mairaw]

Awesome @morganbr! The doc source for this is in this other repo:
https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System/HashCode.xml

Basically, where you see a To be added string, we need to replace that with actual content (remarks are optional).

[ChrisMaddock]

@jcdickinson - Thank you!! 🎉

[jcdickinson]

Pleasure :)