add a jsonata example, readme

Author: cckim

transforms/filter/README.md

@@ -0,0 +1,28 @@
+### Tranforms: Filtering
+
+## ECMAScript
+
+The `ecmascript` argument is great for writing filters.
+See https://stepzen.com/docs/custom-graphql-directives/directives#ecmascript for more information on `ecmascript`.
+We are picturing a real-life scenario in which you call a backend using the `endpoint` argument.
+See https://stepzen.com/docs/connecting-backends/how-to-connect-a-rest-service for more information on `@rest`.
+
+### Quick try
+```
+stepzen deploy
+stepzen request '{customer(name: "John Doe") {id name}}'
+```
+
+## JSONata
+
+JSONata transforms provdes an alternate method for filtering
+customer_1 uses the `[ ... ]` filter to return all "customers" (`$`) that
+contain `name = the argument name`
+
+The outer array constructor `[]` is used to defeat singleton sequence equivalence.
+
+### Quick try
+```
+stepzen deploy
+stepzen request '{customer_1(name: "John Doe") {id name}}'
+```