[boot_rom] Add more descriptive message on successful boot

Fixes #590

Signed-off-by: Silvestrs Timofejevs <silvestrst@lowrisc.org>
diff --git a/sw/device/boot_rom/boot_rom.c b/sw/device/boot_rom/boot_rom.c
index 7d3c8cf..776afbc 100644
--- a/sw/device/boot_rom/boot_rom.c
+++ b/sw/device/boot_rom/boot_rom.c
@@ -34,7 +34,7 @@
     return rv;
   }
 
-  LOG_INFO("Jump!\n");
+  LOG_INFO("Boot ROM initialisation has completed, jump into flash!\n");
   while (!uart_tx_empty()) {
   }
   try_launch();