RFR: Cleaning up headers and examples

[Iris Clark]

On Mon, 22 Aug 2022 15:22:54 GMT, Jesper Wilhelmsson <jwilhelm at openjdk.org> wrote:

> * Make all headers follow the same style
> * Make code examples use ~~~ instead of four space indentation
> * Fix email adresses to be actual adresses
> * Add link to jtreg FAQ
> * Add comment about the name space for noreg-labels

Marked as reviewed by iris (Reviewer).

-------------

PR: https://git.openjdk.org/guide/pull/90