Add /help prompt to initial toolbar help text

[rolandwalker]

Description

This is the first step on advertising forward-slash commands.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .