metastability comment

spi_master.v

@@ -44,7 +44,13 @@ spi_master
 );
 
 `ifndef SPI_MASTER_NO_READ
-/* MISO is almost always an external wire, so buffer it. */
+/* MISO is almost always an external wire, so buffer it.
+ * This might not be necessary, since the master and slave do not respond
+ * immediately to changes in the wires, but this is just to be safe.
+ * It is trivial to change, just do
+ *    wire read_miso = miso;
+ */
+
 reg miso_hot = 0;
 reg read_miso = 0;