- Minor wording fixes. (igor -y)
- Mention poudriere, and poudriere-devel.
- Explain what the test build targets will do.

Differential Revision: https://reviews.freebsd.org/D654
Reviewed by:	wblock
Sponsored by:	Absolight


git-svn-id: svn+ssh://svn.freebsd.org/doc/head@45542 c2e8774f-c49f-e111-b436-862b2bbc8956