zulip-botserver: Document use of environment var in README.md

Author: alexmv

zulip_botserver/README.md

@@ -1,16 +1,29 @@
 ```
 zulip-botserver --config-file <path to botserverrc> --hostname <address> --port <port>
-
 ```
 
 Example: `zulip-botserver --config-file ~/botserverrc`
 
 This program loads the bot configurations from the
-config file (botserverrc here) and loads the bot modules.
+config file (`botserverrc`, here) and loads the bot modules.
 It then starts the server and fetches the requests to the
 above loaded modules and returns the success/failure result.
 
-Please make sure you have a current botserverrc file with the
-configurations of the required bots.
-Hostname and Port are optional arguments. Default hostname is
-127.0.0.1 and default port is 5002.
+The `--hostname` and `--port` arguments are optional, and default to
+127.0.0.1 and 5002 respectively.
+
+The format for a configuration file is:
+
+    [helloworld]
+    key=value
+    [email protected]
+    site=http://localhost
+    token=abcd1234
+
+Is passed `--use-env-vars` instead of `--config-file`, the
+configuration can instead be provided via the `ZULIP_BOTSERVER_CONFIG`
+environment variable.  This should be a JSON-formatted dictionary of
+bot names to dictionary of their configuration; for example:
+
+    ZULIP_BOTSERVER_CONFIG='{"helloworld":{"email":"[email protected]","key":"value","site":"http://localhost","token":"abcd1234"}}' \
+      zulip-botserver --use-env-vars