Add explanation how to use makefile.vc
diff --git a/makefile.vc b/makefile.vc
index 1cacd2f..fecc0ee 100644
--- a/makefile.vc
+++ b/makefile.vc
@@ -1,6 +1,12 @@
# Makefile for Visual Studio
# Written by Krzysztof Kowalczyk (http://blog.kowalczyk.info)
# This code is in public domain.
+# Use it like this from command line:
+# * add Visual Studio tools to your %PATH%
+# * nmake -f makefile.vc TARGET=rel
+# or
+# * nmake -f makefile.vc TARGET=dbg
+# * the result is perftest.exe in either rel or dbg directory
CC = cl.exe
LD = link.exe
