Makefile: document noconfig_targets variable

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
diff --git a/Makefile b/Makefile
index 5f348b2..089989c 100644
--- a/Makefile
+++ b/Makefile
@@ -125,6 +125,7 @@
 # Need to export it, so it can be got from environment in children (eg. mconf)
 export BR2_VERSION_FULL := $(BR2_VERSION)$(shell $(TOPDIR)/support/scripts/setlocalversion)
 
+# List of targets and target patterns for which .config doesn't need to be read in
 noconfig_targets := menuconfig nconfig gconfig xconfig config oldconfig randconfig \
 	defconfig %_defconfig allyesconfig allnoconfig silentoldconfig release \
 	randpackageconfig allyespackageconfig allnopackageconfig \