Fix broken wiki links

The old links to wiki has been broken after we moved wiki to the documentation folder.
The links are updated to pointing to the new documentation location.

Author: zhenlan

Diff for: CONTRIBUTING.md

@@ -1,11 +1,8 @@
 # Contributing
 
-See [Contributing] on the wiki for information about coding styles, source structure, making
+See [Contributing](Documentation/contributing.md) for information about coding styles, source structure, making
 pull requests, and more.
 
-[Contributing]: https://github.com/dotnet/wcf/wiki/Contributing
 # Developers
 
-See the [Developer Guide] for details about developing in this repo.
-
-[Developer Guide]: https://github.com/dotnet/wcf/wiki/Developer-Guide
+See the [Developer Guide](Documentation/developer-guide.md) for details about developing in this repo.

Diff for: README.md

@@ -26,9 +26,9 @@ Want to get more familiar with what's going on in the code?
 
 Looking for something to work on? The list of [up-for-grabs issues](https://github.com/dotnet/wcf/labels/up%20for%20grabs) is a great place to start. See some of our guides for more details:
 
-* [Contributing Guide](https://github.com/dotnet/wcf/wiki/Contributing)
-* [Developer Guide](https://github.com/dotnet/wcf/wiki/Developer-Guide)
-* [Issue Guide](https://github.com/dotnet/wcf/wiki/Issue-Guide)
+* [Contributing Guide](Documentation/contributing.md)
+* [Developer Guide](Documentation/developer-guide.md)
+* [Issue Guide](Documentation/issue-guide.md)
 
 You are also encouraged to start a discussion by filing a [New Issue](https://github.com/dotnet/wcf/issues/new).