Add a README file.

Change-Id: I03060f9e3d5ab0f2366f364a9371ccfb18c7d9b1

README

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+Gerritbot is an IRC bot that will notify IRC channels of Gerrit events.
+
+To install Gerritbot run `python setup.py install` from within the repository's
+root directory.
+
+To run Gerritbot `$PATH/gerritbot /path/to/config`. $PATH is usually something
+like /usr/local/bin and /path/to/config should be whatever path you have hidden
+the config at.
+
+Gerritbot has two configuration files. The first configures the IRC server and
+Gerrit server details and is the config file whose path you pass to gerritbot
+when starting the bot. It should look like:
+  [ircbot]
+  nick=NICKNAME
+  pass=PASSWORD
+  server=irc.freenode.net
+  port=6667
+  channel_config=/path/to/yaml/config
+  
+  [gerrit]
+  user=gerrit2
+  key=/path/to/id_rsa
+  host=review.example.com
+  port=29418
+
+The second configures the IRC channels and the events and projects that each
+channel is interested in. This config file is written in yaml and should look
+like:
+  example-channel1:
+      events:
+        - patchset-created
+        - change-merged
+      projects:
+        - example/project1
+        - example/project2
+      branches:
+        - master
+        - development
+  example-channel2:
+      events:
+        - change-merged
+      projects:
+        - example/project3
+        - example/project4
+      branches:
+        - master