Update TRG instructions

[afontani]

Pull Request Description

Update the TRG local build instructions for some clarity.

Related Pull Requests

[related PRs from different repositories]

Related Issues

[What issue(s) is the PR addressing]

Checklist

Required:

• Add to the [changelog_dev.rst file](https://github.com/NREL/resstock/tree/develop/docs/read_the_docs/source/changelog/changelog_dev.rst)
• No unexpected regression test changes on CI (comparison artifacts have been checked)
• Update documentation (one is required)
  • Technical reference guide
  • [Technical development guide](https://github.com/NREL/resstock/tree/develop/docs/technical_development_guide)

Optional (not all items may apply):

• Tests (and test files) have been updated
• Supporting resource files have been updated (related to resstock-estimation)
  • data dictionary
  • source report
  • options saturation
  • options_lookup
• openstudio tasks.rb update_measures has been run

[lixiliu]

Some suggestions. Thanks!