add basic readme

README.md

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+# Prometheus edge trigger
+
+Trigger http requests a set delay after an edge in a prometheus query.
+
+## Example
+
+Given 2 wifi enabled switches that have their state logged into prometheus,
+automatically turn off `switch2` 5 minutes `switch1` is turned off.
+
+```toml
+[prometheus]
+url = "http://prometheus"
+
+[[trigger]]
+name = "Delay swtich"
+
+[trigger.condition]
+query = "switch_state{instance=\"$instance\"}"
+from = 1
+to = 0
+params.instance = { type = "mdns", service = "_switch-http._tcp.local", host = "switch1" }
+
+[trigger.action]
+method = "PUT"
+params.host = { type = "mdns", service = "_switch-http._tcp.local", host = "switch2" }
+url = "http://$host/off"
+delay = 300
+```