added Information for journal partitions

additional to the needed update in the documentation i had created a note in the graylog.conf about extra partitions for the journal

ref: #2348

misc/graylog.conf

@@ -331,6 +331,11 @@ message_journal_enabled = true
 
 # The directory which will be used to store the message journal. The directory must me exclusively used by Graylog and
 # must not contain any other files than the ones created by Graylog itself.
+#
+# ATTENTION:
+#           If you create a seperate Partition for the journal and use a Filesystem that create directories like 'los+found'
+#           you need to create a subdirectory for your journal.
+#           The Logfile will show a message that your journal is corrupt and Graylog will not start. 
 message_journal_dir = data/journal
 
 # Journal hold messages before they could be written to Elasticsearch.