[Mu] communicate intent of methods Str and gist

Author: moritz

lib/Mu.pod

@@ -32,14 +32,19 @@ Returns C<False> on the type object, and C<True> otherwise
 
     multi method Str()   returns Str
 
-Returns implementation-defined identifier.
+Returns a string representation of the invocant, inteded to be machine
+readable.
 
 =head2 gist
 
     multi sub    gist(Mu) returns Str
     multi method gist()   returns Str
 
-Returns result of using C<.perl> method on current object.
+Returns a string representation of the invocant, optimized for
+fast recognition by humans.
+
+The default C<gist> method in C<Mu> re-dispatches to the C<perl> method,
+but many built-in classes override it to something more specific.
 
 =head2 perl