document include order

Author: nerdralph

README.md

@@ -3,7 +3,7 @@ This library replaces Arduino AVR Core functions with smaller and faster version
 The Arduino Blink example sketch built for the Uno takes 924 bytes of flash, but only needs 196 bytes with ArduinoShrink.
 
 ## Usage
-Download [a release](https://github.com/nerdralph/ArduinoShrink/releases), and extract the files into your Arduino/libraries folder.  Select ArduinoShrink from the Sketch, Include Library menu.  This will replace several Arduino functions with smaller and faster versions.  The Arduino pin number must be known at compile time if you are using this library.
+Download [a release](https://github.com/nerdralph/ArduinoShrink/releases), and extract the files into your Arduino/libraries folder.  Select ArduinoShrink from the Sketch, Include Library menu.  This will replace several Arduino functions with smaller and faster versions. When using multiple libraries, ArduinoShrink must be the last library included in the sketch code. 
 
 ## Design and Implemenation
 I've written <a href="http://nerdralph.blogspot.com/2021/04/honey-i-shrunk-arduino-core.html">a blog post</a> discussing the implementation details of ArduinoShrink.  Version 0.7.0 supports manipulation of pins that are not known at compile-time.  When the pin is known at compiletime, digitalWrite() will still compile to a single "sbi" or "cbi" instruction.