As described in https://golang.org/s/generatedcode, Go has
a formalized format that should be used to indicate that a
file is generated.

Matching that format helps linters to skip generated files;

From https://golang.org/s/generatedcode (https://github.com/golang/go/issues/13560#issuecomment-288457920);

> Generated files are marked by a line of text that matches the regular expression, in Go syntax:
>
> ^// Code generated .* DO NOT EDIT\.$
>
> The `.*` means the tool can put whatever folderol it wants in there, but the comment
> must be a single line and must start with `Code generated` and end with `DO NOT EDIT.`,
> with a period.
>
> The text may appear anywhere in the file.

This patch updates the template used for our generated types
to match that format.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>