Working on branch https://gitlab.cern.ch/cms-analysis/general/HiggsDNA/-/commits/spring_cleaning_documentation.

As pointed out by Clemens in #236, the documentation should be improved and examples should be updated. We should aim for the structure

• Installation

• Main Concepts

• Processors (short description of each one)

• Ingredients and Systematics
• 
Workload distribution
• Postprocessing

• Examples (move JEC to other category), for both processors and postprocessing
• 
Instructions for Developers