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.

NOTE: Documents fail to build during checks because of references to documents that won't exist until this is merged.

Unrelated fixes:

• Documentation version number now fetched from buildozer/__init__.py. Addresses Buildozer docs report wrong version #1738
• Implemented many/all of the formatting changes from Add syntax highlighting to the README #1708.
• Copy-edit of documents.
  • Contents of Contributing.rst moved to CONTRIBUTING.md
  • Removed installation instructions from README.md, so there is only one
    version.
  • Added Recipes description to RST documentation
  • Removed broken index page

CHECKLIST

• CONTRIBUTING.md
  [x] If repo takes user contributions, is present
  [x] In root dir (not .github dir)
  [x] Explains relationship to Kivy, if unclear.
  [x] Refers to kivy/kivy Contribution Guidelines.
  SHOULD TAKE THE CONVERTED COPY OF THE RST.

• 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.md

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

• FAQ.md
  [x] 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 Documentation exists, mention it.
  [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, including:
  [x] Backers
  [x] Sponsors
  [x] GitHub contributors
  [x] Contributor Covenant
  [x] PyPI Version
  [x] PyPI Python Version
  [x] Build/Test status

  [x] Displays all contributors to the repo.
  [x] Displays backers
  [x] Displays top sponsors.

• RST documentation, if present
  [x] Describes the project.
  [x] Describes its place in the Kivy sibling projects.
  [x] Mentions (Kivy/Kivy) Contact Us link.
  [x] Mentions LICENSE.
  [x] Mentions CONTRIBUTING
  [x] Mentions FAQ
  [x] conf.py mentioned Kivy Team and other contributors
  - copyright, latex_documents, man_pages, texinfo documents

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

• setup.py/cfg, if present and on PyPI
  [x] Supplies description to PyPI
  [x] Supplies Python versions to PyPI
  [x] Supplies Documentation, if any, to PyPI

[misl6]

Love this call to action!

[misl6]

We have a minor typo (left a suggestion).

Regarding installation docs: I see that some parts are outdated, but we will do a rework once a new python-for-android is released.

(And [for the records] we had a discussion about buildozer future here: #1663 (comment))

[misl6]

LGTM. Thank you!