Suggestion: Include SMP build instructions in page on configuring/building kernel

[Stefan Blachmann]

Hello,

just a suggestion: In the handbook page about configuring/building
kernel, where I landed first, there is no mention that one can do
parallel building.

I learned of this feature not before I upgraded to Master, after the bug
in syscons got fixed.

(Btw, big thanks and kudos to Matt :)  The fix seems work fine! And
thank you for telling me to pkg upgrade, too! Haven't thought of that...)


I think this passage in the Upgrading page
(https://www.dragonflybsd.org/docs/handbook/Upgrading/)

"*Note:* You may use a concurrent build..." really deserves to be copied
to the configure/build kernel page
(https://www.dragonflybsd.org/docs/handbook/ConfigureKernel/).

Because, I didn't know of that feature from FreeBSD!

And it's just great! Building with all cores instead of just one... I am
just amazed! I am so happy to finally trying DragonFly :)

Kudos and thanks to you all who made DragonFly!

Stefan