Fix comment in palloc

sys/kern/palloc.c

@@ -96,6 +96,9 @@ PAlloc_AddRegion(uintptr_t start, uintptr_t len)
      * PageInfo table isn't initialized on the first call to this function.  We 
      * must allocate a temporary table that will be copied into the XMem region 
      * inside PAlloc_LateInit.
+     *
+     * Note that the PageInfo table is invalid for regions that are not added 
+     * to the free list such as MMIO regions.
      */
     if (pageInfoTable == NULL) {
 	// Physical Address Offsets