Document Array.elems

Include info on .elems of shaped arrays, per:
https://irclog.perlgeek.de/perl6/2017-05-24#i_14631924
https://irclog.perlgeek.de/perl6/2017-05-24#i_14631943

Author: zoffixznet

doc/Type/Array.pod6

@@ -94,6 +94,23 @@ Example:
     say @a.elems;               # OUTPUT: «6␤»
     say @a;                     # OUTPUT: «[a b c d e f]␤»
 
+=head2 method elems
+
+Defined as:
+
+    method elems(Array:D: --> Int:D)
+
+Returns the number of elements in the invocant. Throws C<X::Cannot::Lazy>
+exception if the invocant L<is lazy|/routine/is-lazy>. For shaped arrays,
+returns the outer dimension; see L<shape> if you need information for
+all dimensions.
+
+    say [<foo bar ber>] .elems; # OUTPUT: «3␤»
+    say (my @a[42;3;70]).elems; # OUTPUT: «42␤»
+    
+    try [-∞...∞].elems;
+    say $!.^name;               # OUTPUT: «X::Cannot::Lazy␤»
+
 =head2 method clone
 
 Defined as: