add note on using HIP_PLATFORM to force hcc path

docs/markdown/hip_faq.md

@@ -106,3 +106,9 @@ HIP is a source-portable language that can be compiled to run on either the HCC
 HIP is a portable C++ language that supports a strong subset of the CUDA run-time APIs and device-kernel language. It's designed to simplify CUDA conversion to portable C++. HIP provides a C-compatible run-time API, C-compatible kernel-launch mechanism, C++ kernel language and pointer-based memory management.
 
 A C++ dialect, hc is supported by the AMD HCC compiler. It provides C++ run time, C++ kernel-launch APIs (parallel_for_each), C++ kernel language, and several memory-management options, including pointers, arrays and array_view (with implicit data synchronization). It's intended to be a leading indicator of the ISO C++ standard.
+
+### What if I have a CUDA SDK installed but want to use HCC?
+If HIP sees the CUDA SDK installed at /usr/local/cuda, it assumes the platform is nvcc.  Sometimes this isn't what you want - you can force HIP to recognize the platform by setting HIP_PLATFORM to hcc (or nvcc)
+```
+export HIP_PLATFORM=hcc
+```