Suggestion for clarification of makeopts in linux build instructions

[Walter Dnes]

I suggest inserting an additional item in https://developer.palemoon.org/build/linux/
"Basic Dependencies" to clarify the optimum makeopts jobs number.

========================================================================
* mk_add_options MOZ_MAKE_FLAGS="-jN"
where N should be the LOWER of the two following constraints

1) The number of logical CPUs (including hyperthreads) on your system

2) One half of the number of gigabytes in the "MemAvailable:" line in /proc/meminfo. This will vary from machine to machine, and even on the same machine, depending on whether or not a GUI is running, and if you're running a "heavy desktop". Note: the output from /proc/meminfo is in kilobytes. It can be re-formatted to more readable output with the command...

</proc/meminfo numfmt --field 2 --from-unit=Ki --to=iec | sed "s/ kB//g"
========================================================================

My documentation sources...
1) https://wiki.gentoo.org/wiki/MAKEOPTS

2) man proc_meminfo

MemAvailable %lu (since Linux 3.14)
An estimate of how much memory is available for starting new applications, without swapping.