Add example on how to use gpart before growfs.  While here, reorder examples
so that the simplest one comes first.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274741 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Uniformly refer to a file system as "file system".

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274742 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f