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

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

Reviewed by:	bcr
Approved by:	bcr (doc)
Approved by:	krion (mentor, implicit), mat (mentor, implicit)
Differential Revision:	https://reviews.freebsd.org/D18682

share/man/man7/ports.7

@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 20, 2018
+.Dd December 30, 2018
 .Dt PORTS 7
 .Os
 .Sh NAME
@@ -537,11 +537,33 @@ The default ports directory.
 The big Kahuna.
 .El
 .Sh EXAMPLES
-Build and install Emacs:
-.Bd -literal -offset indent
-cd /usr/ports/editors/emacs
-make install
+.Bl -tag -width 0n
+.It Sy Example 1\&: No Building and Installing a Port
+.Pp
+The following command builds and installs Emacs.
+.Bd -literal -offset 2n
+.Li # Ic cd /usr/ports/editors/emacs
+.Li # Ic make install
 .Ed
+.It Sy Example 2\&: No Installing Dependencies with Xr pkg 8
+.Pp
+The following examples shows how to build and install a port without having to
+build its dependencies.
+Instead, the dependencies are downloaded via
+.Xr pkg 8 .
+.Bd -literal -offset 2n
+.Li # Ic make missing | xargs pkg install --automatic --yes
+.Li # Ic make install
+.Ed
+.Pp
+It is especially useful, when the dependencies are costly
+in time and resources to build
+.Pq like Pa lang/rust .
+The drawback is that
+.Xr pkg 8
+offers only packages built with the default set of
+.Va OPTIONS .
+.El
 .Sh SEE ALSO
 .Xr make 1 ,
 .Xr make.conf 5 ,