add cover sheet example, correct typos

[CHCRowley]

Proposed Changes

Changed cover sheet example to use the penguins dataset, and laid out in the same format as the 'starting out' tutorial:

• basic examples in documented code chunks
• image of example output
• full code in collapsible code chunk

Fixed minor typos in Cover.md and 'starting out' example

Related Issues

• Related to Review examples #312

Pre-requisites

This section may not be fully required if the branch is not merging into main.
Please indicate items that aren't necessary and why, with comments around incomplete checks.

• Version number has been incremented, according to SemVer
• Changelog has been updated, listing changes to this version. Use the keep a changelog format
• New features are tested
• New features are documented using the numpydoc docstring format
• Other relevant package documentation is updated
• For new functionality, examples are included in the docs or a feature request has
  been made for it/them.

[Sara-Jade-O]

Cover sheet example is clear and easy to follow - happy to approve