Add comment re use of libavrdude

src/libavrdude.h

@@ -35,6 +35,19 @@
 #include "libavrdude-avrintel.h"
 #undef  LIBAVRDUDE_INCLUDE_INTERNAL_HEADERS
 
+/*
+ * The libavrdude library contains useful functions for programming
+ * Microchip's 8-bit AVR microprocessors. The command line program avrdude
+ * was written using this library; its source code is a good example of how
+ * to use the library. Out of necessity libavrdude routinely changes
+ * PROGRAMMER, AVRPART and other structures to keep up with new programmers
+ * and with new parts and programming interfaces from Microchip. Any
+ * application that uses this library should ensure that it links to a
+ * libavrdude binary that is compatible with this header file, ideally the
+ * version that was shipped together with this header file or one that was
+ * compiled from source together with the application.
+ */
+
 typedef uint32_t pinmask_t;
 /*
  * Values returned by library functions.