Have a default .deployignore file

[GaryJones]

Suggestion to add a .deployignore file that contains a few default typical files such as phpcs.xml.dist variants, or directories like tests/.

Not only would this encourage better awareness of this supported feature, it would act as a real example, as well as reducing the amount of typical items that would be pushed to production sites.

With comments in it, and a reference to our fuller documentation, it would be easy for client developers to amend, or simply delete if they didn't need it.