rrdtool: add license info

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/rrdtool/rrdtool.mk

@@ -6,6 +6,9 @@
 
 RRDTOOL_VERSION = 1.2.30
 RRDTOOL_SITE = http://oss.oetiker.ch/rrdtool/pub
+RRDTOOL_LICENSE = GPLv2+ with FLOSS license exceptions as explained in COPYRIGHT
+RRDTOOL_LICENSE_FILES = COPYING COPYRIGHT
+
 RRDTOOL_DEPENDENCIES = host-pkgconf freetype libart libpng zlib
 RRDTOOL_AUTORECONF = YES
 RRDTOOL_INSTALL_STAGING = YES