[v2] tutorial: part 4 updates

[amberleyromo]

typos, language tweaks, fleshed out some supporting screenshot examples.

[sktt]

In what cases is page query preferable over the StaticQuery component? Since the former is limited to top level Pages only, isn’t it safer to always stick to StaticQuery, ie recommend that and just mention that page query exist ?

Disclaimer: I’m a newbie with gatsby

[KyleAMathews]

StaticQueries can't take arguments (currently — it might be possible for them to do this) which means you can use them when you want to change arguments by page e.g. blog post queries should get the argument for the id to the markdown page you want to query.