Improve the documentation of the starters

[wilkinsona]

Via some feedback from @dcoxall, we could do a better job of documenting the starters. I think we're guilty of assuming that people will look in the poms to figure out what each starter does.

A couple of ideas to improve the documentation:

• List each starter with a description of what it contains and when you'd use it
• Add an opinionated section that says if you are building X then you should use starter Y

[dcoxall]

👍 This would be incredibly helpful!

[snicoll]

I wonder if we couldn't do something about that on start.spring.io as well.

[wilkinsona]

I wonder if we couldn't do something about that on start.spring.io as well

+1