Update LICENSE

Added a note on license requirement for CAN-FD

Author: dc42

LICENSE

@@ -1,3 +1,13 @@
+NOTE:
+
+The GNU GENERAL PUBLIC license reproduced below does not confer any rights
+to use the partial ISO CAN-FD implementation for the RP2040 processor that
+this software includes. A license from Robert Bosch Gmbh is required for
+any commercial use of CAN-FD. For the other processors (SAMC21 and SAME5x)
+on which this software supports CAN-FD, the license is already paid for by
+the processor manufacturer (Microchip).
+
+--------------------------------------------------------------------------
                     GNU GENERAL PUBLIC LICENSE
                        Version 3, 29 June 2007