Update Parameter.name and add example, ref #3580

Author: stoned

doc/Type/Parameter.pod6

@@ -22,6 +22,10 @@ on what most of the concepts related to parameters mean.
 
 =head2 method name
 
+Defined as:
+
+    method name(Parameter:D: --> Str:D)
+
 Returns the variable name, which includes
 all L<sigils|/language/variables#Sigils> and
 L<twigils|/language/variables#Twigils>.
@@ -31,7 +35,15 @@ usable by a caller – if it is, it will also appear as an
 L<alias|#method named_names>.  Often, the name will be chosen descriptively
 as a form of self-documentation.
 
-If the parameter is anonymous, C<Nil> will be returned.
+If the parameter is anonymous, an empty string will be returned.
+
+B<Note:> Before Rakudo version 2020.08 the return value for an anonymous
+parameter was C<Nil>.
+
+=for code
+my Signature $sig = :(Str $x, Bool);
+say $sig.params[0].name;                 # OUTPUT: «$x␤»
+say $sig.params[1].name;                 # OUTPUT: «␤»
 
 =head2 method sigil