Three New Chapters for Porters HandBook

[Russell Haley]

Hi,

https://reviews.freebsd.org/D12921

I've posted a patch for three chapters to start the porters handbook an
provide context to new developers. It's been sitting for a while with
nobody looking at it.

If you want to read the new chapters, I've posted them on my (garbage)
website here:  http://envirobotics.ca/portershb/tools-introduction.html

It's a very rough draft and there is quite a bit of formatting problems,
but I think the spirit of the work is apparent.

Thoughts and feedback welcome.

Thanks,
Russ