note about .where field for MIC/SCC

doc/doxygen/chapters/430_mic_scc_support.doxy

@@ -62,6 +62,9 @@ functions have to be globally-visible (i.e. not <c>static</c>) for
 StarPU to be able to look them up, and -rdynamic must be passed to gcc (or
 -export-dynamic to ld) so that symbols of the main program are visible.
 
+If you have used the <c>.where</c> field, you additionally need to add in it
+<c>STARPU_MIC</c> for the Xeon Phi, and/or <c>STARPU_SCC</c> for the SCC.
+
 For non-native MIC Xeon Phi execution, the 'main' function of the application, on the sink, should call starpu_init() immediately upon start-up; the starpu_init() function never returns. On the host, the 'main' function may freely perform application related initialization calls as usual, before calling starpu_init().
 
 For MIC Xeon Phi, the application may programmatically detect whether executing on the sink or on the host, by checking whether the STARPU_SINK environment variable is defined (on the sink) or not (on the host).