Improve installation instructions

Rather than assume the location of the user's sketchbook folder (which may not be correct and is different depending on OS), just tell them how to find the location if they don't already know it. This makes the instructions more simple and less confusing.

Author: per1234

Diff for: README.md

@@ -11,12 +11,10 @@ Tested with the following Arduino IDE versions: 1.6.5-r2,
 ## Installation
 - 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)`.
+- In your Arduino sketchbook directory, create `tools` directory if it doesn't exist yet. You can find the location of your sketchbook directory in the Arduino IDE at **File > Preferences > Sketchbook location**.
+- Unpack the tool into `tools` directory (the path will look like `<sketchbook directory>/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).