update README

README.md

@@ -2,6 +2,23 @@
 
 Mattermost bot.
 
+# Environment Variables
+
+## for bot comms to mattermost server
+
+* `SCO_API_URL`
+* `SCO_WEBSOCKET_URL`
+* `SCO_DEBUG_CHANNEL`
+* `SCO_ACCOUNT_EMAIL`
+* `SCO_ACCOUNT_PASSWORD`
+* `SCO_TEAM_NAME`
+* `SCO_ACCOUNT_USERNAME`
+
+## remote stuff
+
+* `METAR_API_TOKEN` for https://avwx.rest
+* `AIRNOW_API_KEY` for http://www.airnowapi.org
+
 # status
 
 [![Build Status](https://drone.datavi.be/api/badges/sneak/sco/status.svg)](https://drone.datavi.be/sneak/sco)