define correct type of the UInt; show some example usage

doc/Type/UInt.pod6

@@ -1,6 +1,6 @@
 =begin pod
 
-=TITLE class UInt
+=TITLE subset UInt
 
 =SUBTITLE Unsigned Integer (arbitrary-precision)
 
@@ -9,4 +9,20 @@ The C<UInt> is defined as a subset of C<Int>:
 =for code :skip-test
 my subset UInt of Int where * >= 0;
 
+Consequently it can be instantiated or subclassed; however, that shouldn't affect most normal uses.
+
+Some examples of its behavior and uses:
+
+=for code :skip-test
+  my UInt $u = 0xffff_ffff_ffff_ffff_ffff_ffff_ffff_ffff; # 64-bit unsigned value
+  say $u.base(16); # FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF (32 digits)
+  ++$u;
+  say $u.base(16); # 100000000000000000000000000000000 (33 digits!)
+  my Int $i = $u;
+  say $i.base(16); # same
+  say $u.WHAT;     # (UInt)
+  say $i.WHAT;     # (Int)
+  $u = $i;
+  say $u.WHAT;     # (Int)!! a subset of Int is an Int
+  
 =end pod