Add explanation about special characters not allowed in url string

Client.md

@@ -34,7 +34,7 @@ Internally the connection string is parsed and a _config_ object is created with
     var client = new Client('/tmp');  //looks for the socket file /tmp/.s.PGSQL.5432
 ```
 
-Caution : 
+#### Caution : 
 Url strings don't allow to pass special characters like `#`
 If you have some of them in your passord, don't use a connection string, use a config object and pass
 it as { host: 'foo', password: 'blah#blah' }