Attempt to explain ways to declare return type in signature

Author: Altai-man

doc/Type/Signature.pod6

@@ -251,6 +251,19 @@ down the call chain.
     sub bar() returns Int { 1 };
     sub does-not-work(--> Int) { "" }; # throws X::TypeCheck::Return
 
+There are two other ways to declare return type:
+
+    sub foo() of Int { 1 };
+    my Int sub bar { 1 };
+
+C<of> is just the real name of C<returns> keyword, and prefix(C-like) form can be used too. Although any of way is valid, C<-->> form differs from all others: it can handle constant values, while others don't.
+
+=begin code :skip-test
+my 42 sub bad-answer {};       # This will fail.
+sub bad-answer2 returns 42 {}; # This too.
+sub answer(--> 42) { return; } # This doesn't.
+=end code
+
 If the type constraint is a constant expression, it is used as the return value
 of the routine. Any return statement in that routine has to be argumentless.