Created Multiplayer (markdown)

Multiplayer.md

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+**Something to note: multiplayer is a new feature, and still contains a good deal of bugs. You're very likely to encounter them. If that happens, please report it if it hasn't been reported already, and please say if the bug only occurs on multiplayer games.**
+
+OpenRCT2 now has initial support for co-op multiplayer. Using it requires use of the command line. You should open a command line window and navigate to the directory where OpenRCT2.exe is located. Alternatively, you could modify your shortcut (provided it's not a shortcut to the OpenRCT.net launcher).
+
+## Starting the server
+To start the built-in server, you only have to specify a port on which OpenRCT2 should listen for clients. This could be any port, provided it's not in use. Usually higher port numbers cause fewer problems. Also, make sure your firewall accepts connections on that port. If you're behind a router and want to allow clients to your server, set up port forwarding in your router.
+
+To start to server with port 22050 (replace with another value if you wish):
+
+```openrct2.exe --port 22050```
+
+## Starting the client
+To make your client connect to a server, you have to specify the IP of the server and the port on which the server listens. 
+
+To connects to a server with the IP address 192.168.1.102 and listening on port 22050 (replace with the actual values of the server you want to connect to):
+
+```openrct2.exe --server 192.168.1.102 --port 22050```