Document that sequences could be iterated multiple times.

#KT-13115 Fixed

libraries/stdlib/src/kotlin/collections/Sequence.kt

@@ -4,11 +4,20 @@ package kotlin.sequences
  * A sequence that returns values through its iterator. The values are evaluated lazily, and the sequence
  * is potentially infinite.
  *
+ * Sequences can be iterated multiple times, however some sequence implementations might constrain themselves
+ * to be iterated only once. That is mentioned specifically in their documentation (e.g. [generateSequence] overload).
+ * The latter sequences throw an exception on an attempt to iterate them the second time.
+ *
+ * Sequence operations, like [Sequence.map], [Sequence.filter] etc, generally preserve that property of a sequence, and
+ * again it's documented for an operation if it doesn't.
+ *
  * @param T the type of elements in the sequence.
  */
 public interface Sequence<out T> {
     /**
-     * Returns an iterator that returns the values from the sequence.
+     * Returns an [Iterator] that returns the values from the sequence.
+     *
+     * Throws an exception if the sequence is constrained to be iterated once and `iterator` is invoked the second time.
      */
     public operator fun iterator(): Iterator<T>
 }