Nokia RX-51: Add link for u-boot-gen-combined script to README file

This patch updates Nokia RX-51 README file.

Signed-off-by: Pali Rohár <pali@kernel.org>
diff --git a/doc/README.nokia_rx51 b/doc/README.nokia_rx51
index 33c275b..320b5ef 100644
--- a/doc/README.nokia_rx51
+++ b/doc/README.nokia_rx51
@@ -16,6 +16,11 @@
 the appended kernel image will be booted using some generated and some
 stored ATAGs (see boot order).
 
+For generating combined image of u-boot and kernel there is a simple script
+called u-boot-gen-combined. It is available in following repository:
+
+  https://github.com/pali/u-boot-maemo
+
 There is support for hardware watchdog. Hardware watchdog is started by
 NOLO so u-boot must kick watchdog to prevent reboot device (but not very
 often, max every 2 seconds). There is also support for framebuffer display