ports.7: Add an example of getting dependencies without building

[0mp]

Summary

While here, improve formatting of the EXAMPLES section in general.

Test Plan

igor, mandoc

[0mp]

Remove parts of a different patch from the review.

[crees]

I would assume that people with their own repo will understand that the default options case doesn't apply to them, so that final comment is probably OK.

[0mp]

In D18682#398622, @crees wrote:

I would assume that people with their own repo will understand that the default options case doesn't apply to them, so that final comment is probably OK.

+1

[0mp]

Use make missing with pkg install instead of USE_PACKAGE_DEPENDS as USE_PACKAGE_DEPENDS only works when the package archives are already available on the machine to be installed.

[bcr]

Good to have these in the examples, so approved. Thanks for the work!