Add Telnet console authentication docs

docs/topics/telnetconsole.rst

@@ -26,8 +26,21 @@ The telnet console listens in the TCP port defined in the
 the console you need to type::
 
     telnet localhost 6023
+    Trying localhost...
+    Connected to localhost.
+    Escape character is '^]'.
+    Username:
+    Password:  
     >>>
-    
+
+By default Username is ``scrapy`` and Password is autogenerated. The 
+autogenerated Password can be seen on scrapy logs like the example bellow::
+
+    2018-10-16 14:35:21 [scrapy.extensions.telnet] INFO: Telnet Password: 16f92501e8a59326
+
+Default Username and Password can be overriden by the settings 
+:setting:`TELNETCONSOLE_USERNAME` and :setting:`TELNETCONSOLE_PASSWORD`
+
 You need the telnet program which comes installed by default in Windows, and
 most Linux distros.
 
@@ -160,3 +173,24 @@ Default: ``'127.0.0.1'``
 
 The interface the telnet console should listen on
 
+
+.. setting:: TELNETCONSOLE_USERNAME
+
+TELNETCONSOLE_USERNAME
+------------------
+
+Default: ``'scrapy'``
+
+The username used for the telnet console
+
+
+.. setting:: TELNETCONSOLE_PASSWORD
+
+TELNETCONSOLE_PASSWORD
+------------------
+
+Default: ``None``
+
+The password used for the telnet console, default behaviour is to have it
+autogenerated
+