Documentation for config file

README.md

@@ -1,3 +1,25 @@
 # adsms
 
-Send SMS aircraft alerts based on ADS-B data
+Send SMS aircraft alerts based on ADS-B data
+
+## Usage
+
+Copy the configuration file, make any necessary changes, and run:
+
+    ./adsms.py <configuration_file>
+
+## Configuration file
+
+* `textbelt_key`: your [Textbelt](https://textbelt.com) API key
+* `data`: a URL to a readsb/tar1090 `aircraft.json` endpoint
+* `tracker`: a URL to a tar1090 tracker (e.g. https://globe.theairtraffic.com/)
+* `database`: an SQLite file in which to store subscriptions
+* `pid_file`: path to which to write the PID (set to empty string to not write
+  a PID file)
+* `max_age`: maximum age of aircraft pings in seconds; pings older than this
+  will be ignored
+* `min_disappearance`: the minimum time in seconds for which an aircraft must
+  go "off the radar" before disappearing for new pings to trigger notifications
+  again
+* `delay`: time to wait after processing all rules before running the loop
+  again