add basic example, update commentary, add picture

[gisellerosetta]

Proposed Changes

• Reformats the basic usage example to be chunked up
• Combines some parts of the code to try and make it look a little simpler
• Rewrites some commentary
• Adds a picture
• Renames files to be more consistent/easier to navigate

Related Issues

• Fixes Update basic usage example #302

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 NA
• Changelog has been updated, listing changes to this version. Use the keep a changelog format NA
• New features are tested NA
• New features are documented using the numpydoc docstring format NA
• 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. NA

[ldavies99]

Revised getting started guide looks clear and easy to follow. Happy for this to merge.