Clean up README

[julienschmidt]

Let's make the README more readable.

Current ideas:

• Less inline code (formatting)
• Format the DSN params as a HTML table
• Add DSN param input values (table column)

[arnehormann]

Or let's keep the inline code - which I consider helpful - but split it into README.md (introduction) and one of HOWTO.md / TUTORIAL.md / USAGE.md / EXAMPLE.md. We can also add a narrative to the latter.
I also think it could be a nice touch to move the wiki examples to play.golang.org (or their own pages in the wiki) and only host a description and a link there.

[arnehormann]

And if you think that's feasible, we should probably rename this issue "improve documentation" 😁

[julienschmidt]

Oh don't get me wrong... I don't want to remove the code, it is just about the eye-distracting formatting 😉

[julienschmidt]

Fixed by 589f54c