[doc] Explicitly state block form can only be used at compile time

[grr]

The docs currently imply that the block form syntax is only available at compile-time:

It is prototyped to take a subroutine reference as an argument. Thus, it can be called in block form:

But I think it needs to be explicitly stated that loading Capture::Tiny at runtime necessitates wrapping the block in an anonymous sub: Capture::Tiny::capture(sub { ... }).

Found somebody else who ran into the same issue: https://www.perlmonks.org/?node_id=870439

Edit: found another one: https://www.perlmonks.org/?node_id=1210478