DOC: Write a short sentence as heading for the rayon methods

Author: bluss

src/rayon/map.rs

@@ -152,7 +152,11 @@ impl<'a, K: Sync + Send, V: Send> IndexedParallelIterator for ParIterMut<'a, K,
 }
 
 
-/// Requires crate feature `"rayon"`.
+/// Parallel iterator methods and other parallel methods.
+///
+/// The following methods **require crate feature `"rayon"`**.
+///
+/// See also the `IntoParallelIterator` implementations.
 impl<K, V, S> IndexMap<K, V, S>
     where K: Hash + Eq + Sync,
           V: Sync,

src/rayon/set.rs

@@ -113,7 +113,11 @@ impl<'a, T: Sync> IndexedParallelIterator for ParIter<'a, T> {
 }
 
 
-/// Requires crate feature `"rayon"`.
+/// Parallel iterator methods and other parallel methods.
+///
+/// The following methods **require crate feature `"rayon"`**.
+///
+/// See also the `IntoParallelIterator` implementations.
 impl<T, S> IndexSet<T, S>
     where T: Hash + Eq + Sync,
           S: BuildHasher + Sync,
@@ -401,7 +405,9 @@ impl<'a, T, S1, S2> ParallelIterator for ParUnion<'a, T, S1, S2>
 }
 
 
-/// Requires crate feature `"rayon"`.
+/// Parallel sorting methods.
+///
+/// The following methods **require crate feature `"rayon"`**.
 impl<T, S> IndexSet<T, S>
     where T: Hash + Eq + Send,
           S: BuildHasher + Send,