doc: removed number of jobs from -j option when running make

[thecoolestguy]

Checklist

• make -j test (UNIX), or vcbuild test nosign (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

doc

Description of change

Removing specified number of jobs from -j option in the documentation
steps for running the make command. A '-j' without a number specified
will use the maximum number allowed for any given machine.
Fixes: #8286

[bnoordhuis]

Assuming you're not a troll trying to work a fork bomb into the documentation: make -j without a number puts no upper limit on the level of concurrency, it starts all tasks in parallel.

[Trott]

Running make clean && make distclean && ./configure && make -j puts the load on my machine way up...it peaked in the high 200s, and then build failed with:

make[1]: *** wait: No child processes.  Stop.

Probably best bet is to just standardize everything on make -j8. Smallest changeset too. Just one file.

[imyller]

No objections to closing this PR?

Thank you for your effort and contribution though, @thecoolestguy

[jbergstroem]

Agree on close. make -j is essentially forkbombing. 4 cores on a semi-recent laptop is safe for copy paste scenarios.