Minor: Add some missing documentation to fix CI errors (#6445)

* fix CI errors

* apply suggestion from review

Co-authored-by: ngli-me <107162634+ngli-me@users.noreply.github.com>

---------

Co-authored-by: ngli-me <107162634+ngli-me@users.noreply.github.com>
diff --git a/arrow-string/src/like.rs b/arrow-string/src/like.rs
index 6d82682..5c76d5c 100644
--- a/arrow-string/src/like.rs
+++ b/arrow-string/src/like.rs
@@ -158,7 +158,9 @@
 /// This trait helps to abstract over the different types of string arrays
 /// so that we don't need to duplicate the implementation for each type.
 pub trait StringArrayType<'a>: ArrayAccessor<Item = &'a str> + Sized {
+    /// Returns true if all data within this string array is ASCII
     fn is_ascii(&self) -> bool;
+    /// Constructs a new iterator
     fn iter(&self) -> ArrayIter<Self>;
 }