Broken link to Contributing Guide in README.md of AspNetDocs repo

[dean-e-peterson]

Issue

In the AspNetDocs repository
README.md file,
the link to the Contributing Guide is broken.

Why I am Filing the Issue Here

I am filing this issue in the [AspNetCore.Docs](https://github.com/dotnet/AspNetCore.Docs] repository instead of in the AspNetDocs repository where the issue is because:

• Issues are not allowed in that repository.
• This [AspNetCore.Docs](https://github.com/dotnet/AspNetCore.Docs] repository README.md refers to that AspNetDocs repository for ASP.NET 4.x documentation changes.