explain max_message_size and the fact that changing the value may cau…

…se crashes

server/tinode.conf

@@ -32,8 +32,10 @@
 	"api_key_salt": "T713/rYYgW7g4m3vG6zGRh7+FM1t0T8j13koXScOAj4=",
 
 	// Maximum message size allowed from the clients in bytes (262144 = 256KB).
-	// Intended to prevent malicious clients from sending very large messages in-band
-	// (does not affect out-of-band large files).
+	// Media files with sizes greater than this limit are sent out of band.
+	// Don't change this limit to a much higher value because it would likely cause crashes:
+	// on Android & iOS due to a limit on the SQLite cursor window size;
+	// on the server-side with MySQL adapter due to the limit on the sort buffer size.
 	"max_message_size": 262144,
 
 	// Maximum number of subscribers per group topic.