Add a FAQ entry regarding collapsible form groups (#924)

Refs #920.

README.md

@@ -1813,6 +1813,10 @@ A: Not yet (except for a special case where you can use `oneOf` in [schema depen
 
 A: Probably not. We use Bootstrap v3 and it works fine for our needs. We would like for react-jsonschema-form to support other frameworks, we just don't want to support them ourselves. Ideally, these frontend styles could be added to react-jsonschema-form with a third-party library. If there is a technical limitation preventing this, please consider opening a PR. See also: [#91](https://github.com/mozilla-services/react-jsonschema-form/issues/91), [#99](https://github.com/mozilla-services/react-jsonschema-form/issues/99), [#125](https://github.com/mozilla-services/react-jsonschema-form/issues/125), [#237](https://github.com/mozilla-services/react-jsonschema-form/issues/237), [#287](https://github.com/mozilla-services/react-jsonschema-form/issues/287), [#299](https://github.com/mozilla-services/react-jsonschema-form/issues/299), [#440](https://github.com/mozilla-services/react-jsonschema-form/issues/440), [#461](https://github.com/mozilla-services/react-jsonschema-form/issues/461), [#546](https://github.com/mozilla-services/react-jsonschema-form/issues/546), [#555](https://github.com/mozilla-services/react-jsonschema-form/issues/555), [#626](https://github.com/mozilla-services/react-jsonschema-form/issues/626), and [#623](https://github.com/mozilla-services/react-jsonschema-form/pull/623).
 
+### Q: Is there a way to "collapse" fields, for instance to show/hide individual fields?
+
+A: There's no specific built-in way to do this, but you can write your own FieldTemplate that supports hiding/showing fields according to user input. We don't yet have an example of this use, but if you write one, please add it to the "tips and tricks" section, above. See also: [#268](https://github.com/mozilla-services/react-jsonschema-form/issues/268), [#304](https://github.com/mozilla-services/react-jsonschema-form/pull/304), [#598](https://github.com/mozilla-services/react-jsonschema-form/issues/598), [#920](https://github.com/mozilla-services/react-jsonschema-form/issues/920).
+
 ## License
 
 Apache 2