Update out-of-date Sampling section of docs

[joseph-robertson]

Pull Request Description

In response to https://unmethours.com/question/96702/resstock-sampling-file/.

Checklist

Not all may apply:

• Tests (and test files) have been updated
• Documentation has been updated
  • If related to resstock-estimation, checklist includes data dictionary, source report, options_lookup.
  • If changes to project_testing tsvs, checklist includes yml_precomputed, yml_precomputed_outdated, yml_precomputed_weight
• Changelog has been updated
• openstudio tasks.rb update_measures has been run
• No unexpected regression test changes on CI (checked comparison artifacts)