[SwipeRefresh] Make scrollable requirements clearer in docs (#407)

* Improve SwipeRefresh kdoc

Added some info about scrollable content

* Add SwipeRefresh scrollable para to guide

* Fix spotless

* Fix typo

docs/swiperefresh.md

@@ -36,6 +36,19 @@ SwipeRefresh(
 
 The full example, including the view model implementation can be found [here](https://github.com/google/accompanist/blob/main/sample/src/main/java/com/google/accompanist/sample/swiperefresh/DocsSamples.kt).
 
+The content needs to be 'scrollable' for `SwipeRefresh()` to be able to react to swipe gestures. Layouts such as [`LazyColumn`][lazycolumn] are automatically scrollable, but others such as [`Column`][column] are not. In those instances, you can provide a [`Modifier.verticalScroll`][verticalscroll] modifier to that content like so:
+
+``` kotlin
+SwipeRefresh(
+    // ...
+) {
+    Column(Modifier.verticalScroll(rememberScrollState())) {
+        // content
+    }
+}
+```
+
+
 ### Indicating a refresh without swiping
 
 As this library is built with a seperate state object, it's easy to display a refreshing indicator without a swipe to triggering it.
@@ -124,4 +137,7 @@ Snapshots of the development version are available in [Sonatype's `snapshots` re
   [api_swiperefreshindicator]: ../api/swiperefresh/swiperefresh/com.google.accompanist.swiperefresh/-swipe-refresh-indicator.html
   [api_swiperefresh]: ../api/swiperefresh/swiperefresh/com.google.accompanist.swiperefresh/-swipe-refresh.html
   [api_rememberstate]: ../api/swiperefresh/swiperefresh/com.google.accompanist.swiperefresh/remember-swipe-refresh-state.html
-  [sample_customindictor]: https://github.com/google/accompanist/blob/main/sample/src/main/java/com/google/accompanist/sample/swiperefresh/SwipeRefreshCustomIndicatorSample.kt
+  [sample_customindictor]: https://github.com/google/accompanist/blob/main/sample/src/main/java/com/google/accompanist/sample/swiperefresh/SwipeRefreshCustomIndicatorSample.kt
+  [lazycolumn]: https://developer.android.com/reference/kotlin/androidx/compose/foundation/lazy/package-summary#LazyColumn(androidx.compose.ui.Modifier,androidx.compose.foundation.lazy.LazyListState,androidx.compose.foundation.layout.PaddingValues,kotlin.Boolean,androidx.compose.foundation.layout.Arrangement.Vertical,androidx.compose.ui.Alignment.Horizontal,androidx.compose.foundation.gestures.FlingBehavior,kotlin.Function1)
+  [column]: https://developer.android.com/reference/kotlin/androidx/compose/foundation/layout/package-summary#Column(androidx.compose.ui.Modifier,androidx.compose.foundation.layout.Arrangement.Vertical,androidx.compose.ui.Alignment.Horizontal,kotlin.Function1)
+  [verticalscroll]: https://developer.android.com/jetpack/compose/gestures#scroll-modifiers

swiperefresh/src/main/java/com/google/accompanist/swiperefresh/SwipeRefresh.kt

@@ -182,18 +182,22 @@ private class SwipeRefreshNestedScrollConnection(
 }
 
 /**
- * A layout which implements the swipe-to-refresh pattern.
+ * A layout which implements the swipe-to-refresh pattern, allowing the user to refresh content via
+ * a vertical swipe gesture.
  *
- * The layout can be used whenever the user has the ability to refresh content via a vertical
- * swipe gesture.
+ * This layout requires its content to be scrollable so that it receives vertical swipe events.
+ * The scrollable content does not need to be a direct descendant though. Layouts such as
+ * [androidx.compose.foundation.lazy.LazyColumn] are automatically scrollable, but others such as
+ * [androidx.compose.foundation.layout.Column] require you to provide the
+ * [androidx.compose.foundation.verticalScroll] modifier to that content.
  *
  * Apps should provide a [onRefresh] block to be notified each time a swipe to refresh gesture
  * is completed. That block is responsible for updating the [state] as appropriately,
  * typically by setting [SwipeRefreshState.isRefreshing] to `true` once a 'refresh' has been
  * started. Once a refresh has completed, the app should then set
  * [SwipeRefreshState.isRefreshing] to `false`.
  *
- * If an app wishes to show just the progress animation, outside of a swipe refresh, it can
+ * If an app wishes to show the progress animation outside of a swipe gesture, it can
  * set [SwipeRefreshState.isRefreshing] as required.
  *
  * This layout does not clip any of it's contents, including the indicator. If clipping