Include comment directive that makes inlining refreshable

[kentfredric]

As per: Perl-Toolchain-Gang/ExtUtils-MakeMaker#203

It would be nice to inject a statement inside a #!start -> #!end block recording what the original inclusion was, to enable it being repeated in an automated fashion.

Being able to extract and apply such statements is additional effort, but it should be straight forward
enough to start injecting them now so consumers will get the update benefits when they're available.