CFR: add an example of manually fetching distfiles to Porter's Handbook

[Buganini]

2011/12/4 Rene Ladan <r.c.ladan at gmail.com>:
> What about turning it into a bsd.<somefile>.mk target, e.g. :
> WEBSITE=some-website
> DISTFILES=same-as-usual
> MANUAL_DISTFILES=distfile1 distfile2 ...

What if there are multiple sites/path and files?
Multiple sites might be uncommon, but multiple path in same site is an issue.

Regards,
Buganini