bridge_with_irc: Add a brief documentation.

zulip/integrations/bridge_with_irc/README.md

@@ -0,0 +1,20 @@
+# IRC <--> Zulip bridge
+
+## Usage
+
+```
+./irc-mirror.py --irc-server=IRC_SERVER --channel=<CHANNEL> --nick-prefix=<NICK> --stream=<STREAM> [optional args]
+```
+
+`--stream` is a Zulip stream.
+
+Specify your Zulip API credentials and server in a ~/.zuliprc file or using the options.
+
+Note that "_zulip" will be automatically appended to the IRC nick provided
+
+## Example
+
+```
+./irc-mirror.py --irc-server=irc.freenode.net --channel='#python-mypy' --nick-prefix=irc_mirror --stream='test here' \
+                --site="https://chat.zulip.org" --user=<bot-email> --api-key=<bot-api-key>
+```