Gatsby: [v2] Document how to create a "SEO" component using <StaticQuery>

[KyleAMathews]

This is a common problem people run into — it's much more straightforward in v2 with <StaticQuery> so let's improve the docs for this.

[jlengstorf]

FYI, this is built. I just have to write up the docs.

https://github.com/jlengstorf/marisamorby.com/blob/master/src/components/SEO/SEO.js

[spences10]

Hey @jlengstorf do you want me to expand on the documentation you have for this already if I can get it workingnfor my own purposes first?

I could go through setting it up with the Gatsby blog starter I guess

[jlengstorf]

@spences10 Yes! That would be amazing — I definitely have not had time to write it up. 😅

[DSchau]

See #9075 for the implementation of this. Can close when it's merged!