Improve discoverability of the quick start page

[ItsHarper]

• Adds quick start link to the homepage, in a "tip" admonition
• Changes the title of the tutorials admonition from "Want a tutorial?" to "Want a tutorial for something specific?"
  • My intention was to help distinguish the concept of the quick start guide (an overview of the whole app) and the tutorials (targeted guides for specific use cases)
• Adds quick start link to the sidebar (the second entry, beneath "home")