Add note to restore API host

Author: ashton-huxtable

src/connections/sources/catalog/libraries/website/javascript/custom-proxy.md

@@ -247,3 +247,7 @@ analytics.load({
    cdnSettings: {...} // object from https://cdn.segment.com/v1/projects/<YOUR_WRITE_KEY>/settings'
  })
 ```
+
+## Restore the API Host to the Segment Default
+
+If you wish to restore the proxied API host to it's original value, navigate to the Source >> Settings >> Analytis.js tab, and then scroll down until you see the Host address field. Under the field, there will be small blue text that says 'Restore to a default value'. Click 'Restore' and then the 'Save' button. Any changes made to the CDN host must be update manually in your code.