Add OS X directory explanation

Hey, 

I am new to the Arduino IDE and I have spent about 2 hours to find where the tools directory is on OS X. Thought it might be helpful for other mac users to see how to use the plugin on OS X.

Author: ccostel

README.md

@@ -12,9 +12,11 @@ Tested with the following Arduino IDE versions: 1.6.5-r2,
 - Make sure you use one of the supported versions of Arduino IDE and have ESP8266 core installed.
 - Download the tool archive from [releases page](https://github.com/esp8266/arduino-esp8266fs-plugin/releases/latest).
 - In your Arduino sketchbook directory, create tools directory if it doesn't exist yet.
-- Unpack the tool into tools directory (the path will look like `<home_dir>/Arduino/tools/ESP8266FS/tool/esp8266fs.jar)`.
+- Unpack the tool into tools directory (the path will look like `<home_dir>/Arduino/tools/ESP8266FS/tool/esp8266fs.jar)` *.
 - Restart Arduino IDE.
 
+* On the OS X create the tools directory in ~/Documents/Arduino/ and unpack the files there.
+
 ## Usage
 - Open a sketch (or create a new one and save it).
 - Go to sketch directory (choose Sketch > Show Sketch Folder).