add more description to using reporting as a service

x-pack/examples/reporting_example/README.md

@@ -1,6 +1,33 @@
-Example Reporting integration!
-==============================
+# Example Reporting integration!
 
-Use this example code to understand how to add a "Generate Report" button to a Kibana page. 
+Use this example code to understand how to add a "Generate Report" button to a
+Kibana page. This simple example shows that the end-to-end functionality of
+generating a screenshot report of a page just requires you to render a React
+component that you import from the Reportinng plugin.
 
-Coming soon: control which users are able to use the button based on Feature Controls.
+A "reportable" Kibana page is one that has an **alternate version to show the data in a "screenshot-friendly" way**. The alternate version can be reached at a variation of the page's URL that the App team builds.
+
+A "screenshot-friendly" page has **all interactive features turned off**. These are typically notifications, popups, tooltips, controls, autocomplete libraries, etc.
+
+Turning off these features **keeps glitches out of the screenshot**, and makes the server-side headless browser **run faster and use less RAM**.
+
+The URL that Reporting captures is controlled by the application, is a part of
+a "jobParams" object that gets passed to the React component imported from
+Reporting. The job params give the app control over the end-resulting report:
+
+- Layout
+  - Page dimensions
+  - DOM attributes to select where the visualization container(s) is/are. The App team must add the attributes to DOM elements in their app.
+  - DOM events that the page fires off and signals when the rendering is done. The App team must implement triggering the DOM events around rendering the data in their app.
+- Export type definition
+  - Processes the jobParams into output data, which is stored in Elasticsearch in the Reporting system index.
+  - Export type definitions are registered with the Reporting plugin at setup time.
+
+The existing export type definitions are PDF, PNG, and CSV. They should be
+enough for nearly any use case.
+
+If the existing options are too limited for a future use case, the AppServices
+team can assist the App team to implement a custom export type definition of
+their own, and register it using the Reporting plugin API **(documentation coming soon)**.
+
+---