Delete -j from make setup and document use of -jN and -j in r…

…eadme (zeldaret#804)

* Add nproc to make setup

* Add cross-platform nproc equivalents

* Scrap that, just ditch -j in makefile altogether

* Clarified thread advice

Makefile

@@ -203,7 +203,7 @@ distclean: clean
 	$(MAKE) -C tools distclean
 
 setup:
-	$(MAKE) -C tools -j
+	$(MAKE) -C tools
 	python3 fixbaserom.py
 	python3 extract_baserom.py
 	python3 extract_assets.py

README.md

@@ -151,6 +151,13 @@ md5sum: WARNING: 1 computed checksum did NOT match
 
 This means that the built ROM isn't the same as the base one, so something went wrong or some part of the code doesn't match.
 
+**NOTE:** to speed up the build, you can either:
+* pass `-jN` to `make setup` and `make`, where N is the number of threads to use in the build. The generally-accepted wisdom is to use the number of virtual cores your computer has.
+* pass `-j` to `make setup` and `make`, to use as many threads as possible, but beware that this can use too much memory on lower-end systems.
+
+Both of these have the disadvantage that the ordering of the terminal output is scrambled, so for debugging it is best to stick to one thread (i.e. not pass `-j` or `-jN`).
+
+
 ### Cygwin
 
 If you want to use Cygwin, you will need to: