sink method documented in Seqs. Closes #2028

Author: JJ

doc/Type/Seq.pod6

@@ -118,9 +118,21 @@ C<repeat { body } while cond> loops.
 The third form enables C-style looping by calling a third callback,
 C<&afterward>, after each call to C<&body>.
 
+=head2 method sink
+
+Defined as:
+
+    method sink(--> Nil)
+
+Calls L<C<sink-all>|/routine/sink-all> if it is an C<Iterator>, C<sink> if the Sequence is a list.
+
+    say (1 ... 1000).sink; # OUTPUT: «Nil␤»
+
+This is something you might want to do for the side effects of producing those values.
+
 =head2 method skip
 
-Defined As:
+Defined as:
 
     multi method skip(Int() $n = 1 --> Seq)