-# are appropriate for particular setups (OS, CPU, whatever). Make
-# a Config-foo file for setup foo, then set Config to be a symlink
-# to Config-foo.
+# are appropriate for particular setups (OS, ARCH, whatever). Make a
+# Config-foo file for setup foo, then arrange for Config to be a
+# symlink to Config-foo.
+# Commonly used variables in Config are: ARCH_SRC, ASSEM_SRC, GC_SRC,
+# OS_SRC, OS_LIBS, OS_OBJS, OS_CLEAN_FILES