Adds images to examples

[skrawcz]

To make it simpler to grok what an example is doing. We should be leveraging this fact to always make it clear that you can provide this documentation if you use Hamilton!

Also fixes some minor bugs I found with one of the examples.

Changes

• adds DAG images
• fixes bug in data loader example
• fixes typo in one doc string

How I tested this

• ran the examples

Notes

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.

[elijahbenizzy]

Looked over, everything looks good!