Document Routine.cando

Fixes #749

doc/Type/Routine.pod6

@@ -43,6 +43,17 @@ Returns C<True> if the routine is a multi sub or method.
 Returns a list of multi candidates, or a one-element list with itself
 if it's not a multi
 
+=head2 method cando
+
+    method cando(Capture $c)
+
+Returns a possibly-empty list of candidates that can be called with the
+given L<Capture|/type/Capture>, ordered by narrowest candidate first. For
+methods, the first element of the Capture needs to be the invocant:
+
+    .signature.say for "foo".^can("comb")[0].cando: \(Cool, "o");
+    # (Cool $: Str $matcher, $limit = Inf, *%_)
+
 =head2 method wrap
 
     method wrap(Routine:D: &wrapper)