Add a pointer to 7.2 in 4.2 and/or 4.6

[ocroquette@…]

Right now the new port maintainer is not really guided from one step to the other to create a new port, especially the jump to the last one (chapter 7).

For people who wants to submit a new portfile from scratch, it would be useful to have a link from 4.2 and/or 4.6.

Or may be even a quick howto referencing 4. and 7.