doc: wrong link in ADL_SDK readme.txt.

https://github.com/veox/sgminer/issues/7

Author: veox

ADL_SDK/readme.txt

@@ -1,4 +1,4 @@
 Please insert AMD ADL files adl_defines.h adl_sdk.h adl_structures.h here.
 
 They can be found at
-http://developer.amd.com/tools-and-sdks/heterogeneous-computing/amd-accelerated-parallel-processing-app-sdk/downloads/
+http://developer.amd.com/tools-and-sdks/graphics-development/display-library-adl-sdk/