Update default config

Rename default config to match the binary name and add config exampe.

Change-Id: Iabfc78c95e904af7372f10c195b2b979675d34f3
Related: SYS#2655
diff --git a/osysmon_main.c b/osysmon_main.c
index 98859ed..5983212 100644
--- a/osysmon_main.c
+++ b/osysmon_main.c
@@ -70,7 +70,7 @@
 };
 
 
-static const char *config_file = "osysmon.cfg";
+static const char *config_file = "osmo-sysmon.cfg";
 struct osysmon_state *g_oss;