In classtut.rakudoc, add links plus a clarifying sentence about trait is built(False) (#4694)

Author: schultzdavid

doc/Language/classtut.rakudoc

@@ -166,7 +166,7 @@ again), you can change the attribute declaration:
 =for code
 has Bool $.done is rw;
 
-The C<is rw> trait causes the generated accessor method to return a container
+The L<C<is rw>|/type/Attribute#trait_is_rw> trait causes the generated accessor method to return a container
 so external code can modify the value of the attribute.
 
 =head2 C<is built> trait
@@ -177,10 +177,11 @@ has &!callback is built;
 X<|Types,traits;Types,is built>
 By default private attributes are not automatically set by the default constructor. (They are private after
 all.) In the above example we want to allow the user to provide the initial value but keep the attribute
-otherwise private. The C<is built> trait allows to do just that.
+otherwise private. The L<C<is built>|/type/Attribute#trait_is_built> trait allows to do just that.
 
-One can also use it to do the opposite for public attributes, i.e. prevent them to be automatically
-initialized with a user provided value, but still generate the accessor method:
+One can use the same trait C<is built> to do the opposite for public attributes, i.e. prevent them from being
+automatically initialized with a user-provided value, but still generate the accessor method. This is done by giving
+the argument C<False> to the trait:
 
 =for code
 has $.done is built(False);