Document Mixy.pick/.grab/.kxxv (#3149)

Potential fix for D#2205 #2205
pending resolution of rakudo/rakudo#2109

Co-authored-by: Zoffix Znet <zoffixznet@users.noreply.github.com>

Author: JJ

doc/Type/Mixy.pod6

@@ -19,6 +19,27 @@ C<Mixy> are L<Real|/type/Real>s rather than L<Int|/type/Int>s.
 Similar to a L<Bag|/type/Bag>.roll, but with C<Real> weights rather than integral
 ones.
 
+=head2 method pick
+
+    method pick($?)
+
+Throws an exception. The feature is not supported on the type, since there's no
+clear value to subtract from non-integral weights, to make it work.
+
+=head2 method grab
+
+    method grab($?)
+
+Throws an exception. The feature is not supported on the type, since there's no
+clear value to subtract from non-integral weights, to make it work.
+
+=head2 method kxxv
+
+    method kxxv()
+
+Throws an exception. The feature is not supported on the type, since there's no
+clear value to subtract from non-integral weights, to make it work.
+
 =head1 See Also
 
 L<Sets, Bags, and Mixes|/language/setbagmix>