GitLab

* doc reorg and edits

* Update wrapper.rst with changes from PR #1098

* Update docs/dockerhub.rst
Co-authored-by: Bartlomiej Wroblewski <bwroblewski10@gmail.com>

* Update docs/index.rst
Co-authored-by: Bartlomiej Wroblewski <bwroblewski10@gmail.com>

* Update docs/what-is-ck.rst
Co-authored-by: Bartlomiej Wroblewski <bwroblewski10@gmail.com>

* Update docs/what-is-ck.rst

Restored to 4 bullets, with additional text for wrapper.
Co-authored-by: Bartlomiej Wroblewski <bwroblewski10@gmail.com>

* Update docs/Contributors_Guide.rst
Co-authored-by: Lisa <lisajdelaney@gmail.com>

* Update API_Reference_Guide.rst

using sentence case for title

* updated index structure per Lisa

* separate docker hub and tutorial

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Co-authored-by: Bartlomiej Wroblewski <bwroblewski10@gmail.com>
Co-authored-by: Lisa <lisajdelaney@gmail.com>
Co-authored-by: Illia Silin <98187287+illsilin@users.noreply.github.com>