dev guide: Point out to document correct header

docs/source/developer_guide.md

@@ -372,9 +372,9 @@ template void raft::expensive<float>(float);
 
 **Design considerations**: 
 
-1. In the `-ext.cuh` header, do not include implementation headers. Only include function parameter types and types that are used to instantiate the templates. If a primitive takes custom parameter types, define them in a separate header called `<primitive_name>_types.hpp` (see [Common Design Considerations](https://github.com/rapidsai/raft/blob/7b065aff81a0b1976e2a9e2f3de6690361a1111b/docs/source/developer_guide.md#common-design-considerations)).  
+1. In the `-ext.cuh` header, do not include implementation headers. Only include function parameter types and types that are used to instantiate the templates. If a primitive takes custom parameter types, define them in a separate header called `<primitive_name>_types.hpp`. (see [Common Design Considerations](https://github.com/rapidsai/raft/blob/7b065aff81a0b1976e2a9e2f3de6690361a1111b/docs/source/developer_guide.md#common-design-considerations)).
 
-2. Keep docstrings in the `-inl.cuh` header, as it is closer to the code. Remove docstrings from template definitions in the `-ext.cuh` header.
+2. Keep docstrings in the `-inl.cuh` header, as it is closer to the code. Remove docstrings from template definitions in the `-ext.cuh` header. Make sure to explicitly include public APIs in the RAFT API docs. That is, add `#include <raft/expensive.cuh>` to the docs in `docs/source/cpp_api/expensive.rst` (instead of `#include <raft/expensive-inl.cuh>`).
 
 3. The order of inclusion in `expensive.cuh` is extremely important. If `RAFT_EXPLICIT_INSTANTIATE_ONLY` is not defined, but `RAFT_COMPILED` is defined, then we must include the template definitions before the `extern template` instantiations.