memorialize index building process

[gbinal]

Let's glance back at the code and update this together, maybe this Tuesday?

Relevant files -

• https://github.com/GSA/federal-website-index/blob/main/process/index-creation.md
• https://github.com/GSA/site-scanning-documentation/blob/main/pages/index_narrowing_steps.md
• https://github.com/GSA/federal-website-index/tree/main/data/snapshots#readme
• https://github.com/GSA/federal-website-index/blob/main/data/site-scanning-target-url-list-analysis.csv

Drafting this here...