Fix a doc typo and clarify the render performance considerations

src/lib.rs

@@ -179,18 +179,22 @@ pub use nucleo;
 /// ```
 ///
 /// ## Performance considerations
-/// Generally speaking, this crate assumes that the [`Render`] implementation is quite
-/// fast. For each item, the [`Render`] implementation is first called to generate the match
-/// objects, and then if the item is not ASCII, [`Render`] is called again in order to render
-/// the interactive picker screen with the relevant matches.
-///
-/// In particular, very slow [`Render`] implementations which output non-ASCII will reduce
-/// interactivity of the terminal interface. A crude rule of thumb is that rendering a single
+/// In the majority of situations, performance of the [`Render`] implementation is only relevant
+/// when sending the items to the picker, and not for generating the match list interactively. In
+/// particular, in the majority of situations, [`Render::render`] is called exactly once per item
+/// when it is sent to the picker.
+///
+/// The **only** exception to this rule occurs the value returned by [`Render::render`] contains
+/// non-ASCII characters. In this situation, it can happen that *exceptionally slow* [`Render`]
+/// implementations will reduce interactivity. A crude rule of thumb is that rendering a single
 /// item should take (in the worst case) at most 100μs. For comparison, display formatting a
 /// `f64` takes around 100ns.
 ///
-/// If this is not the case for your type, it is highly recommended to cache the render
-/// computation:
+/// 100μs is an extremely large amount of time in the vast majority of situations. If after
+/// benchmarking you determine that this is not the case for your [`Render`] implementation,
+/// and moreover your [`Render`] implementation outputs (in the majority of cases) non-ASCII
+/// Unicode, you can internally cache the render computation (at the cost of increased memory
+/// overhead):
 /// ```
 /// # use nucleo_picker::Render;
 /// pub struct Item<D> {
@@ -506,7 +510,7 @@ impl<T: Send + Sync + 'static, R: Render<T>> Picker<T, R> {
     }
 
     /// Returns an [`Observer`] containing up-to-date [`Injector`]s for this picker. For example,
-    /// this is the channel to which new injectors will be sent when the picker process a
+    /// this is the channel to which new injectors will be sent when the picker processes a
     /// [restart event](Event::Restart). See the [`Event`] documentation for more detail.
     ///
     /// Restart events are not generated by this library. You only need this channel if you