update/add some documentation.

Author: brean

README.md

@@ -2,26 +2,44 @@ Getting Started:
 ----------------
 
 ```python
->>> import libardrone
->>> drone = libardrone.ARDrone()
+>>> from libardrone import ardrone
+>>> drone = ardrone.ARDrone()
 >>> # You might need to call drone.reset() before taking off if the drone is in
 >>> # emergency mode
 >>> drone.takeoff()
 >>> drone.land()
 >>> drone.halt()
 ```
 
-The drone's property `image` contains always the latest image from the camera.
-At present this is in the format of a numpy array with dimensions (width, height, 3).
-This may change in future.
+Using the drone's function `get_image()` you can get the latest image from the camera.
+At present this is in the format of a numpy array with dimensions (width, height, 3) that can be used e.g. in opencv:
+
+
+```python
+>>> import cv2
+>>> cv2.namedWindow('image', cv2.WINDOW_AUTOSIZE)
+>>> while True:
+>>>      # get image data as numpy array
+>>>      img = drone.get_image()
+>>>      # show image using opencv
+>>>      cv2.imshow("image", cv2.cvtColor(img, cv2.COLOR_BGR2RGB))
+>>>      if cv2.waitKey(1) & 0xFF == ord('q'): # press 'q' to quit
+>>>          break
+```
+
 The drone's property `navdata` contains always the latest navdata.
+You can for example get the current battery charge from that:
 
+```
+>>> bat = drone.navdata.get(0, dict()).get('battery', 0)
+>>> print('Battery: %i%%' % bat)
+```
 
-Demo:
------
+Demo (pygame):
+--------------
 
 There is also a demo application included which shows the video from the drone
-and lets you remote-control the drone with the keyboard:
+and lets you remote-control the drone with the keyboard (you need pygame for it to work):
 
     RETURN      - takeoff
     SPACE       - land
@@ -52,7 +70,7 @@ Requirements:
 
 This software was tested with the following setup:
 
-  * Python 2.7.6
+  * Python 2.7.13
   * Unmodified AR.Drone firmware 2.0
 
 
@@ -62,4 +80,3 @@ License:
 This software is published under the terms of the MIT License:
 
   http://www.opensource.org/licenses/mit-license.php
-