FreeBSD/doc 558e48e (r53309)en_US.ISO8859-1/books/porters-handbook/special chapter.xml

Porter's Handbook: Suggest using Poudriere in using-cargo section

Also improve section title.

Approved by:    mat
Differential Revision:  https://reviews.freebsd.org/D21253
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+6-11en_US.ISO8859-1/books/porters-handbook/special/chapter.xml
+6-111 files

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