Improve Cool's description/summary

Fixes #1095

Author: zoffixznet

doc/Type/Cool.pod6

@@ -2,13 +2,18 @@
 
 =TITLE class Cool
 
-=SUBTITLE Value that can be treated as a string or number interchangeably
+=SUBTITLE Object that can be treated as either a string or number
 
     class Cool is Any { }
 
 C<Cool>, also known as the B<C>onvenient B<OO> B<L>oop, is a base class
-for strings, numbers and other built-in classes that you are supposed to use
-mostly interchangeably.
+employed by a number of built-in classes that can be meaningfully coerced
+to a string or a number. For example, an L<Array> can be used in mathematical
+operations, where its numerical representation is the number of elements it
+contains. At the same time, it can be concatenated to a string, where its
+stringy representation is all of its elements L<joined|/routine/join> by
+a space. Because L<Array> is L<Cool>, the appropriate coercion happens
+automatically.
 
 Methods in C<Cool> coerce the invocant to a more
 specific type, and then call the same method on that type. For example both