Add headers to examples.

Author: phillipjohnston

examples/default_to_serial/default_to_serial.ino

@@ -1,3 +1,12 @@
+/**
+* This sketch demonstrates using the ArduinoPrintf library with the default setup,
+* which requires no initialization. The Serial class will be used as the output
+* for the ArduinoPrintf library.
+*
+* You are still responsible for initializing the Print class in setup(), the
+* ArduinoPrintf library will not do that for you.
+*/
+
 #include <ArduinoPrintf.h>
 
 void setup() {

examples/override_putchar/override_putchar.ino

@@ -1,3 +1,10 @@
+/**
+* This sketch demonstrates the ability to override the ArduinoPrintf library's
+* default implementation of _putchar() with a custom user implementation.
+* You can do anything you want in your _putchar() function: output to multiple ports,
+* filter data, add extra characters, etc.
+*/
+
 #include <ArduinoPrintf.h>
 
 void setup() {

examples/specify_print_class/specify_print_class.ino

@@ -1,3 +1,12 @@
+/**
+* This sketch demonstrates using the ArduinoPrintf library with a custom
+* Print class of your choice. Call printf_init() with the desired output class.
+* Any class which has Print as a base class can be used.
+*
+* You are still responsible for initializing the Print class in setup(), the
+* ArduinoPrintf library will not do that for you.
+*/
+
 #include <ArduinoPrintf.h>
 
 void setup() {