Rollup merge of rust-lang#52477 - frewsxcv:frewsxcv-iter-short, r=alexcrichton

Clarify short-circuiting behvaior of Iterator::zip.

Fixes rust-lang#52279.

Author: kennytm

src/libcore/iter/iterator.rs

@@ -384,7 +384,9 @@ pub trait Iterator {
     ///
     /// In other words, it zips two iterators together, into a single one.
     ///
-    /// If either iterator returns [`None`], [`next`] will return [`None`].
+    /// If either iterator returns [`None`], [`next`] from the zipped iterator
+    /// will return [`None`]. If the first iterator returns [`None`], `zip` will
+    /// short-circuit and `next` will not be called on the second iterator.
     ///
     /// # Examples
     ///