Update links in docs to GPUOpen and to Doxygen

[ROCm/hip-tests commit: afac6a2c4a]

projects/hip-tests/samples/0_Intro/bit_extract/README.md

@@ -2,3 +2,5 @@
 
 Show an application written directly in HIP which uses platform-specific check on __HIP_PLATFORM_HCC__ to enable use of 
 an instruction that only exists on the HCC platform.
+
+See related [blog](http://gpuopen.com/platform-aware-coding-inside-hip/) demonstrating platform specialization.