[Docs]: Move example walkthrough from `example/` folder into Read the Docs

[harryswift01]

Documentation Update

The worked example currently lives in a standalone example/ folder at the repo root (a README.txt plus input/output files) instead of being part of the published Read the Docs site.

Why Is This Needed?

Anyone relying only on the published docs (e.g. from a Conda install) never sees this worked example, since it only exists in the git repo. Bringing it into the docs makes it discoverable alongside the rest of the usage documentation, and removes a stray top-level folder from the repo.

Suggested Changes

• Add a new docs/source/examples.rst page containing the worked competition calculation walkthrough (command, inputs, outputs), with the input/output files and figure available via Sphinx :download: links
• Move the actual example files (pbr322.toy.fa, one_line.pbr322.toy.fa, IRF .html outputs, pbr322.toy.compete.txt, all.eps) into docs/source/_static/examples/
• Add examples to index.rst's toctree
• Update source-usage.rst's existing "Example calculation" section to cross-reference the new page instead of describing the old directory
• Remove the now-empty example/ folder