docs: add working table quick start

[sato820]

Closes #24

This updates the table documentation with a reproducible quick start and fixes a few example mismatches that can make the demos look broken:

• adds a step-by-step quick start using local data
• fixes the example template id so it matches templateID
• fixes clear-link HTML from class=".clear" to class="clear"
• uses data keys that match sortable table headers
• updates the demo and site links to the current jlord.computer URLs
• adds troubleshooting notes for blank output, sorting, filtering and pagination
• explains why starting from local data avoids the public demo's old spreadsheet dependency

I could not run the browserified demo in this environment because this checkout does not include installed npm dependencies, but the changes are documentation-only and were checked against index.js behavior. I also validated the README examples for matching template ids, clear-link classes and stale demo links.