Fix link to c++ developer guide from CONTRIBUTING.md (#12084)

Noticed this link was broken when poking around, I think this should fix it.

Authors:
  - https://github.com/brandon-b-miller

Approvers:
  - David Wendt (https://github.com/davidwendt)

URL: #12084

CONTRIBUTING.md

@@ -382,7 +382,7 @@ You can skip these checks with `git commit --no-verify` or with the short versio
 
 ## Developer Guidelines
 
-The [C++ Developer Guide](cpp/docs/DEVELOPER_GUIDE.md) includes details on contributing to libcudf C++ code.
+The [C++ Developer Guide](cpp/doxygen/developer_guide/DEVELOPER_GUIDE.md) includes details on contributing to libcudf C++ code.
 
 The [Python Developer Guide](https://docs.rapids.ai/api/cudf/stable/developer_guide/index.html) includes details on contributing to cuDF Python code.