Improve documentation following feedback from use

[jacques-lebourgeois]

Prerequisites

• I have searched for duplicate or closed feature requests
• I have read the contributing guidelines

Proposal

Improve documentation to give examples of the following feedback:

• How do I use a colour that is not in one of the colour palettes provided?
• How do you customise the content or part of the content of the popup or tooltip?
• More detail on how to use Apache Echart's internal popup or tooltip manager (with the ODS design)

Motivation and context

These requests for changes to the documentation are the result of questions from users of the library.