A Raspberry Pi install page; the build's job count is the core count (from dev 6f49f498c3c6)

doc/install/macos_source_install.md

@@ -90,6 +90,13 @@ make -C com               # optimized (-O3) by default; libklammertext.so + sks/
 ktext -s '@eval 1 + 1 @' -d  # smoke test — prints 2
 ```
 
+The build compiles as many files at once as the machine has cores (`-j`
+with the core count, in the variable `JOBS`), and more jobs than cores
+gain nothing: a compile keeps a core busy, so eight jobs on a four-core
+machine only take turns. On a machine with little memory the optimizing
+compiler may run out of it and report `out of memory allocating`; if so,
+`make -C com JOBS=2`, or `JOBS=1`: slower, and it finishes.
+
 (For a debug build with AddressSanitizer, intended for development, prefix
 `DEBUG=1`: `DEBUG=1 make -C com`.)