Small changes on the color recognition and readme

[vncprado]

I just found a small typo on the Python script for color recognition, and I also included instructions in the readme to clone https://github.com/JenniferBuehler/general-message-pkgs which is required by the example.

[vimior]

@vncprado
Thank you very much for your support and suggestions, but the structure of the gripper of Lite6 is different from that of xarm, and it does not support moveit control for the time being, so this example is not applicable to Lite6.

[vimior]

@vncprado
In addition, cv2.boxPoints is only available in opencv3.0. It was cv2.cv.BoxPoints before. Here it is judged according to the python version. Later we will decide which function to use according to the cv version.

[vncprado]

Sounds good! Thanks for the feedback.