app_java: added note in makefile about generating the readme on a system without java

modules/app_java/Makefile

@@ -1,6 +1,8 @@
-# 
+#
 # WARNING: do not run this directly, it should be run by the master Makefile
 
+# to generate readme file on a system without java, use DOCBUILD=yes in make command
+
 include ../../Makefile.defs
 auto_gen=
 NAME=app_java.so