Apply minor edits across core docs for enhanced readability

[stichbury]

This is a good issue for anyone interested in docs to the point of applying a style guide to some markdown. There's no rewriting required (just small tweaks) and no knowledge of Vizro is expected.

I think the core docs (and probably vizro-ai docs too) could benefit from a minor edit to improve their readability. This would involve the following steps:

• Creating an informal "lexicon" or style guide (which could be added to the contribution guide)
• Applying this across the docs
• Creating a set of tickets if the readability review throws up a need to make further changes beyond minor word choices

[stichbury]

Style guide is now added to the contribution guide. I've applied it to the Get Started docs and it would be awesome to see it applied to other pages. I will get round to it all in time, but am putting a "Help Wanted" and "Good First Issue" label on this because we could definitely use outside help. For example:

• ensure consistent capitalisation e.g. across section heads
• ensure consistent use of admonitions
• US English throughout
  * bullet capitalisation and full stops
• Oxford commas