Fill index pages with summaries of content inside the sections

[mowies]

Goal

As a user accessing a section from the docs page, I want to understand what that section is about in a short paragraph.

Details

Fill all the index.md pages in the sub-section folders of the docs page with helpful and short paragraphs about the gist of the corresponding section. Also add links to the most important pages in the section.

DoD

• index pages filled with content
• links to most important pages of each section added

Notes

• depends on Copy content to new docs page #2553