Fixed syslog-error, to syslog:error, and referenced a section detailing

tags.

Signed-off-by: Zsolt Gyulai (zgyulai) <zsolt.gyulai@quest.com>

Author: zsoltgyulai94

_includes/doc/admin-guide/options/source-flags.md

@@ -139,7 +139,7 @@
     If the BOM[^1] character is missing, but the message is otherwise UTF-8
     compliant, {{ site.product.short_name }} automatically adds the BOM character to the
     message.
-- *no-piggyback-errors*: On failure, the original message will be left as it was before parsing, the value of `$MSGFORMAT` will be set to `syslog-error`, and a tag will be placed on the message corresponding to the parser's failure.
+- *no-piggyback-errors*: On failure, the original message will be left as it was before parsing, the value of `$MSGFORMAT` will be set to `syslog:error`, and a tag (see Tagging messages) will be placed on the message corresponding to the parser's failure.
 - *piggyback-errors*: On failure, the old behaviour is used (clearing the entire message then syslog-ng will generate a new message in place of the old one describing the parser's error).
 
 [^1]: The byte order mark (BOM) is a Unicode character used to signal the byte-order of the message text.