Add logic starlark example (#7864)

plugins/processors/starlark/README.md

@@ -152,6 +152,9 @@ Attempting to modify the global scope will fail with an error.
 - [ratio](/plugins/processors/starlark/testdata/ratio.star)
 - [rename](/plugins/processors/starlark/testdata/rename.star)
 - [scale](/plugins/processors/starlark/testdata/scale.star)
+- [number logic](/plugins/processors/starlark/testdata/number_logic.star)
+
+Open a [PR](https://github.com/influxdata/telegraf/compare) to add any other useful Starlark examples. 
 
 [specification]: https://github.com/google/starlark-go/blob/master/doc/spec.md
 [string]: https://github.com/google/starlark-go/blob/master/doc/spec.md#strings

plugins/processors/starlark/testdata/number_logic.star

@@ -0,0 +1,9 @@
+# Set  any 'status' field between 1 and 6 to a value of 0
+
+def apply(metric):
+    v = metric.fields.get('status')
+    if v == None:
+        return metric
+    if 1 < v and v < 6:
+        metric.fields['status'] = 0
+    return metric