Mention why you'd want codegen-units = 0 (other than running out of RAM)

config.toml.example

@@ -306,6 +306,9 @@
 #
 #debug = false
 
+# This will make your build more parallel; it costs a bit of runtime
+# performance perhaps (less inlining) but it's worth it.
+#
 # Number of codegen units to use for each compiler invocation. A value of 0
 # means "the number of cores on this machine", and 1+ is passed through to the
 # compiler.