Update README.md

Author: blemasle

README.md

@@ -11,7 +11,8 @@ This library provides full control over the Microchip's [MCP23017](https://www.m
  * Full interrupt support
 
 ## Usage
-Unlike most Arduino library, no default instance is created when the library is included. It's up to you to create one with the appropriate chip I2C address.
+Unlike most Arduino library, no default instance is created when the library is included. It's up to you to create one using the appropriate I2C address based on  MCP23017 `A0`, `A1` and `A2` pins wirings.
+Available addresses go from `0x20` to `0x27`, allowing up to 8 MCP23017 on the same I2C bus.
 
 ```cpp
 #include <Arduino.h>
@@ -32,4 +33,4 @@ Major renames have been performed in v2.0.0 to improve compatibility with a vari
 | `MCP23017_REGISTER`   | `MCP23017Register`        |
 | `MCP23017_INTMODE`    | `MCP23017InterruptMode`   |
 
-In addition to this, every member of the `MCP23017Register` enum were renamed to avoid possible conflicts with macro definitions. `GPIOA` was renamed to `GPIO_A`, `INTCAPA` to `INTCAP_A` and so on...
+In addition to this, every member of the `MCP23017Register` enum were renamed to avoid possible conflicts with macro definitions. `GPIOA` was renamed to `GPIO_A`, `INTCAPA` to `INTCAP_A` and so on...