Improve documentation of power model

[davide-f]

Describe the feature you'd like to see

Beyond improving the documentation of the sector model #1208, the power model may benefit from improvements:

• Revise short tutorial- electric #1340
• Ensure configuration parameters are up to date in documentation #1341
  • To revise the configuration.rst file to ensure the proper configuration parameters are mapped accordingly. For example, in top configuration, custom_rules is missing
  • Check if all power configurations are available in the configtables
• Revise section model customization in readthedocs #1342
  • probably general modelling guidelines is not needed
  • revise basic customization to reflect the renewed config.yaml management of incremental changes and explain to the user that it shall copy from config.default and place in config. yaml
  • Include a section to customize network data information
  • include a section to customize renewable production, though we shall provide better interfaces for this
• description of alternative clustering
• augmented network connections

Please, comment if you identify more to add