Revise the Starters documentation

[stichbury]

Impact from #3158 is that we need to update the page about starters to:

• Explain the new add-ons workflow is superceding their direct usage (if that's the best way to describe what we are doing)
• Remove those that we are sunsetting
• Add any new starters
• Show examples
• Summarise what has changed/what stays the same.

[stichbury]

This has been covered by docs for 0.19 release.