add documentation

README.md

@@ -1,3 +1,47 @@
+## Usage
+
+### Configuration
+
+kapacitor.toml:
+
+```
+[udf]
+[udf.functions]
+  [udf.functions.scale]
+    socket = "/tmp/kapacitor-scale.sock"
+    timeout = "10s"
+```
+
+then start kapacitor-scale like this:
+
+```
+$ kapacitor-scale -
+```
+
+### Example
+
+```
+stream...
+  .scale()
+    .id('rancherServiceId')
+    .when('value > 10')
+    .by('current + 1')
+    .min_instances(2)
+    .max_instances(10)
+    .cooldown('1m')
+```
+
+#### Options
+
+- id: Id of the rancher service to scale
+- when: expression, should evaluate to true
+  (see https://github.com/pk-rawat/gostr)
+- by: expression, should evaluate to a number
+  (see https://github.com/pk-rawat/gostr)
+- max\_instances: maximum instances to scale out
+- max\_instances: minimum instances to scale in
+- cooldown: timeout to wait until next scaling action
+
 ## Tests
 
 $ go test ./handler
@@ -7,3 +51,4 @@ $ go test ./handler
 - start cooldown timer, when service was actually scaled up
 - do not freak out, when rancher service is not available
 - (free up unneeded services, when removed from rancher)
+- procname contains rancher url with credentials! (change argv)