Make doc structure consistent and up-to-date

[Julian-O]

This is part of an effort to make the Kivy sibling projects' documentation
structure consistent and up-to-date.

CHECKLIST

• CONTRIBUTING.md
  [x] If repo takes user contributions, is present
  [x] In root dir (not .github dir)
  [x] Refers to kivy/kivy Contribution Guidelines.

• LICENSE
  [x] If repo takes user contributions, is present.
  [x] Acknowledges the range of years to 2023.
  [x] Acknowledges Kivy Team and other contributors
  [x] Mentions it is an MIT License.

• CODE_OF_CONDUCT.md
  [x] If repo takes user contributions or hosts discussions, is present.
  [x] Refers to kivy/kivy CODE_OF_CONDUCT

• CONTACT.md
  [x] Refers to kivy/kivy CONTACT.md

• FAQ.md
  [NA] If repo is big enough for RST documentation, is present.

• README:
  [x] Is a Markdown file.
  [x] Describes the project.
  [x] Describes its place in the Kivy sibling projects.
  [x] If CONTRIBUTING exists, mentions it.
  [x] If LICENSE exists, mentions it.
  [x] If CODE_OF_CONDUCT exists, mentions it.
  [x] Mentions kivy/kivy CONTACT.md
  [NA] Uses Python syntax colouring for embedded Python code.
  [x] Uses badges to display current status.

• RST documentation, if present
  [NA] Describes the project.
  [NA] Describes its place in the Kivy sibling projects.
  [NA] Mentions LICENSE.
  [NA] Mentions CONTRIBUTING
  [NA] Mentions CODE_OF_CONDUCT
  [NA] Mentions FAQ

• WORKFLOWS
  [NA] NO_RESPONSE.yml is present if the repo has awaiting_reply tag.
  [NA] NO_RESPONSE uses latest script versions.
  [NA] SUPPORT.yml is present if the repo has a support tag.
  [NA] SUPPORT.yml refers to kivy/kivy CONTACT.md

• setup.py/cfg, if present and on PyPI
  [NA] Supplies description to PyPI
  [NA] Supplies Python versions to PyPI
  [NA] Supplies Kivy/Kivy Code of Conduct to PyPI
  [NA] Supplies Contributing Guide to PyPI (local if different to kivy/kivy)
  [NA] Supplies Documentation, if any, to PyPI