add d20 dice roller example

examples/d20.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env shrimp
+# usage: dice <sides>
+
+import math only=random
+import list only=first
+import str only=[replace starts-with?]
+
+sides = $.args | first 
+sides ??= 20
+
+if sides | starts-with? d: 
+  sides = replace sides //\D// ''
+end
+
+sides = number sides 
+
+echo 'Rolling d$sides...'
+random 1 sides | echo