Improve the documentation in the README and the project page

Problem/Motivation

Improve the documentation in the README and the project page

- Clarify dependency on the Matomo reporting API
- Update the readme according to the https://www.drupal.org/docs/develop/managing-a-drupalorg-theme-module-or... →
- add installation instructions
- add configuration instructions. explain exact steps to get module working
- Double check if Matomo UI and module use the same terminology (Auth token vs user token, etc.)
- Use the module name "Matomo on page metrics" consistent (using the same casing) throughout all the documentation and UI labels
- Refer to other modules consistently (using the same casing) throughout all the documentation and UI labels

Steps to reproduce

Read the readme.

Proposed resolution

Improve documentation according to the points above.

Remaining tasks

Do it

User interface changes

See above.

API changes

None

Data model changes

Nope