doc is readonly

Author: gfldex

doc/Type/Signature.pod6

@@ -618,6 +618,12 @@ C<Array> full of C<Scalar>s as described above, C<is raw> will instead cause
 the parameter to produce a C<List>.  Each element of that list will be bound
 directly as raw parameter.
 
+X<|trait,is readonly>
+To explicitely as for a read-only parameter use the C<is readonly> trait.
+Please note that this applies only to the container. The object inside can very
+well have mutator functions and Perl 6 will not enforce immutability on the
+attributes of the object.
+
 Traits can be followed by the where clause:
 
     sub ip-expand-ipv6($ip is copy where m:i/^<[a..f\d\:]>**3..39$/) { }