Adds race/hyper closes #534 refs #2034

doc/Language/statement-prefixes.pod6

@@ -53,6 +53,22 @@ However, with C<eager> as a statement prefix it will run all three iterations in
 the loop, as shown by the printed "Hey", even if we are just requesting the
 first one in a row.
 
+=head2 X<C<hyper>|hyper (statement prefix)>, X<C<race>|race (statement prefix)>
+
+C<hyper> and C<race> use (maybe simultaneous) threads to run different
+iterations in a loop:
+
+=for code
+my $main-thread = $*THREAD.id;
+    my $saw-another-thread = False;
+    race for ^10000 {
+        $saw-another-thread = True if $*THREAD.id != $main-thread;
+    }
+ok $saw-another-thread, 'A race for loop runs the body over threads';
+
+Unless you can come up with a real use case it's probably better that you try
+and reduce your problem to a single data structure and use them in L<method
+form|/routine/hyper>.
 
 =end pod