documentation: fdp-primer: update the build chapter

[kevans]

Summary

Recent changes have renovated the build system, update to reflect those
changes. The changes specifically noted are:

• dc7b79a328f (.ORDER for some parallel safety)
• 127d3f2965d (generate went away, run is no longer the default)
• 7da17aa0103 (top-level Makefile to drive both builds)

The Makefiles have been resynced, slight adjustments to text.

[kevans]

I also went ahead and rendered it for view here: https://people.freebsd.org/~kevans/doc/en/books/fdp-primer/#doc-build

I note that the website build doesn't --minify right now and adjusted the Makefile example; should it?

[lwhsu]

In D28409#635499, @kevans wrote:

I note that the website build doesn't --minify right now and adjusted the Makefile example; should it?

The reason we can't have --minify right now is because it generate broken RSS file so we use www/tidy-html5 port for now.

[debdrup]

Bullet point 4 in the quickstart needs to be removed, since move-shared no longer exists. :)
I don't know if you wanna fix it, but {git-doc-all} doesn't render properly, although that might be due to missing definitions?
The Website Makefile segment also needs to be updated with references to ./shared becoming ../shared/

[carlavilla]

I just made the commit. Thanks for that!