[DOC] fixed rendering in dependencies doc

[templierw]

Reference Issues/PRs

Fixes #3421

What does this implement/fix? Explain your changes.

• Modified introductory sentence with simple enumeration of types;
• Merge the three note blocks into one that uses a list for explaining the types;
• less redundant phrasing

PR checklist

For all contributions

• I've added myself to the list of contributors.
• I've added unit tests and made sure they pass locally.
• The PR title starts with either [ENH], [MNT], [DOC], or [BUG] indicating whether the PR topic is related to enhancement, maintenance, documentation, or bug.

[MatthewMiddlehurst]

I like the style change, though it does not appear to be rendering as intended.

You can check out the change by clicking details on the docs/readthedocs.org:sktime test.

[templierw]

@MatthewMiddlehurst , I couldn't find "details on the docs/readthedocs.org:sktime test". Is it in the repository?

[achieveordie]

@templierw You can check out the built doc here.

This is present on this page itself, the last check docs/readthedocs.org:sktime.

[lmmentel]

@templierw FYI

[GuzalBulatova]

Like the style change, looks like it's being rendered correctly now, nice work!