Docstring for `clustring.py`

[tlentali]

In order to reach the highest pylint note, I added some doc-string in each beginning of each script. But I didn't fill it correctly.

https://github.com/tlentali/pycht/blob/31e3e5323f52eb556648e83d04be304bbf1cec37/pycht/clustering.py#L1-L3

Should be :

To aim of this script is to manage an image.
It can read, reshape, and convert image to float, as well as displaying and writing the picture in a file.  
It also contains a method that can compute a color separation in order to provide the different stencils.

It should serve as a quick reference to all the functions and arguments.

Docstring format :

• what are the most common python docstring formats
• styleguide

[simoneguld]

I can take this one