Added a few more method definitions and an example

doc/Type/Parameter.pod6

@@ -33,6 +33,10 @@ If the parameter is anonymous, C<Nil> will be returned.
 
 =head2 method sigil
 
+Defined as:
+
+    method sigil(Parameter:D:) returns Str:D
+
 Returns a string containing the parameter's sigil, for a looser
 definition of "sigil" than what is considered part of
 the variable's C<name|method name>.  Still returns a sigil even
@@ -72,8 +76,16 @@ Defined as:
 
 Returns C<True> if it's a L<named parameter|/type/Signature#Positional_vs._Named>.
 
+    my Signature $sig = :(Str $x, Bool :$is-named);
+    say $sig.params[0].named;                          # False
+    say $sig.params[1].named;                          # True
+
 =head2 method named_names
 
+Defined as:
+
+    method named_names(Parameter:D:) returns List:D
+
 Returns the list of externally usable names/aliases for a
 L<named parameter|/type/Signature#Positional_vs._Named>.
 
@@ -204,6 +216,10 @@ this parameter, or C<Any> if no default was provided.
 
 =head2 method type_captures
 
+Defined as:
+
+    method type_captures(Parameter:D:) returns List:D
+
 Returns a list of variable names of type captures associated with this
 parameter.  Type captures define a type name within the attached code,
 which is an alias to the type gleaned from the argument during a call.