Refactor README

What's the problem this feature will solve?

Since the README file has become quite large, perhaps it's time we consider refactoring it.

Describe the solution you'd like

• Make README small and concise focusing on important things
• Keep on README description, svg image, installation and basic usage of the pip-tools
• Move the other sections to https://pip-tools.rtfd.io/

References:

• https://github.com/pypa/pip
• https://github.com/pypa/build
• https://github.com/pypa/virtualenv
• https://github.com/pallets/click
• https://github.com/pytest-dev/pytest
• https://github.com/pytest-dev/pytest-asyncio

Alternative Solutions

N/A

Additional context

• https://fosstodon.org/@jamescooke/109954634904286238
• https://hachyderm.io/@jamescooke@fosstodon.org/110125938514902869

/cc @jamescooke