OpenMP offload: add comment explaining workaround for missing kernels command

Author: awnawab

src/core/field_RANKSUFF_module.fypp

@@ -579,6 +579,9 @@ $:offload_macros.detach(ptr=['SELF%DEVPTR'], indent=6)
       CALL SELF%GET_DEVICE_DATA_RDONLY (PTR)
       ALLOCATE (ZZ, MOLD=PTR)
 
+#! OpenMP offload does not have an equivalent for the kernels command,
+#! which means we cannot rely on array notation here and must generate
+#! a nested gang-vector loop. 
 #:for i in range(ft.rank, 0, -1)
 #:set indent = ' ' * (5 + (ft.rank-i)*2)
 #:if i == ft.rank

src/util/field_RANKSUFF_clone_module.fypp

@@ -53,6 +53,9 @@ SUBROUTINE ${ft.name}$_CLONE_ON_${TARGET}$(YL, YR)
   ZR => GET_${TARGET}$_DATA_RDONLY (YR)
   ZL => GET_${TARGET}$_DATA_RDWR (YL)
 
+#! OpenMP offload does not have an equivalent for the kernels command,
+#! which means we cannot rely on array notation here and must generate
+#! a nested gang-vector loop. 
 #:for i in range(ft.rank, 0, -1)
 #:set indent = ' ' * (1 + (ft.rank-i)*2)
 #:if i == ft.rank