Add reference to schematic diagram

Author: richardash1981

README.md

@@ -8,6 +8,7 @@ http://wiringpi.com
 
 For a description of the hardware I wrote these for, see my blog at
 http://eastertrail.blogspot.co.uk/
+and the schematic diagram PushButtonControl-schematic.pdf 
 
-These scripts are under a CC0 license, in other words in the public domain as far as
-permitted by law. You are free to do what you like with them, they are very simple!
+These scripts and files are under a CC0 license, in other words in the public domain as far
+as permitted by law. You are free to do what you like with them, they are very simple!