chore: Add a step to template for signs.json changes

[cmaddox5]

Summary of changes

Asana Ticket: ad-hoc

Added an additional item to the PR checklist. My understanding of signs.json is that the same content needs to live in both signs_ui and realtime_signs. This new item will help new contributors remember to update both.

Reviewer Checklist

• Meets ticket's acceptance criteria
• Any new or changed functions have typespecs
• Tests were added for any new functionality (don't just rely on Codecov)
• This branch was deployed to the staging environment and is currently running with no unexpected increase in warnings, and no errors or crashes (compare on Splunk: staging vs. prod)