busybox-syslog: add more comments to systemd configuration file

Add more comments to the systemd configuration file for busybox's
syslogd utility. The purpose is to easy the life of system administrators.

These comments are mostly derived from the comments in syslogd.c in
busybox.

[YOCTO #5722]

(From OE-Core rev: eba4f2bd2a0becc086f107dbd0d3ec5222c5eed2)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/busybox/files/busybox-syslog.default

@@ -1 +1,25 @@
 OPTIONS="-C"
+# The above option means syslogd will log to 16K shm circular buffer.
+# You could use `logread' to read it.
+
+# All available options are:
+# -O FILE       :      Log to FILE (default:/var/log/messages)
+# -l N          :      Log only messages more urgent than prio N (1-8)
+# -S            :      Smaller output
+# -s SIZE       :      Max size (KB) before rotation (default:200KB, 0=off)
+# -b N          :      N rotated logs to keep (default:1, max=99, 0=purge)
+# -R HOST[:PORT]:      Log to HOST:PORT (default PORT:514)
+# -L            :      Log locally and via network
+# -D            :      Drop duplicates
+# -C[size_kb]   :      Log to shared mem buffer (use logread to read it)
+# -f FILE       :      Use FILE as config (default:/etc/syslog.conf)
+# -m MIN        :      Minutes between mark lines (default:20, 0=off)
+# -K            :      Log to kernel printk buffer (use dmesg to read it)
+
+# Example 1:
+# Log to local file /var/log/mylog
+# OPTIONS="-O /var/log/mylog"
+#
+# Example 2:
+# Log to remote host
+# OPTIONS="-R 192.168.1.1:601"