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.

Unrelated items:

• Readme was vestigial. Wrote description from scratch.

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.

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

• 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 repo's CONTACT.md

• setup.py/cfg, if present and on PyPI
  Note: Template used for Kivy SDK for Windows
  [too hard] Supplies description to PyPI
  [too hard] Supplies Python versions to PyPI
  [x] Supplies Documentation, if any, to PyPI

[misl6]

Hi @Julian-O .

I left some comments, and we need to fix the README before the merge.
If you need some more explanations, feel free to ping me on Discord.

Important note:
Except for macOS scripts, we do not expect "standard users" to use any other feature of kivy-sdk-packager directly.

[misl6]

We're almost there 🏁

I've left some minor comments regarding typos, and outdated content.

[Julian-O]

@misl6: Thanks! Done.

Great news about setting the deploy target. Removed warning from the macOS README too.

[misl6]

LGTM. Thank you!