Adds a readme.

README.md

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+A simple mutli-threaded chat server written in Haskell with support for
+user-to-user private messaging and channels which users can join and
+chat in.
+
+Run server:
+
+```
+$ link <port>
+```
+
+Command to the server over TCP:
+
+```
+$ telnet <host> <port>
+```
+
+Commands sent to the server:
+
+- `LOGIN <username>` Login with the username
+- `QUIT` Quit the server
+- `MSG <username> <message>` Send a private message to a user
+- `JOIN <channel>` Join a channel
+- `LEAVE <channel>` Leave a channel
+- `TELL <channel> <message>` Send a message to a channel
+- `NAMES <channel>` Get names of all users in a channel
+- `PONG` Reply to a ping from the server
+
+Messages from the server:
+
+- `LOGGEDIN <username>` Confirmation of a login
+- `NAMEINUSE <username>` Username is already taken
+- `MSG <username> <message>` A private message from a user
+- `NOSUCHUSER <username>` You tried to send a message to a non-existent user
+- `JOINED <channel> <username>` A user joined the channel you have joined
+- `LEFT <channel> <username>` A user left the channel you have joined
+- `NAMES <channel> <username> <username> ...` Names of all users in a channel
+- `TELL <channel> <username> <message>` A message from a channel you have joined
+- `PING` A ping from the server. Must be replied with a `PONG` command or else
+   the server will disconnect you.