Make more explicit that -e and -f aren't in Perl 6

Author: paultcochrane

lib/Type/IO/FileTestable.pod

@@ -10,10 +10,10 @@
 
 =head2 File Test operators
 
-X<-e> X<:-f>
+X<-e> X<-f>
 
-    -e
-    -f Does not exist in Perl 6. See :e, :f.
+The C<-e> and C<-f> file test operators do not exist in Perl 6. Use instead
+C<:e> and C<:f>.
 
 X<-M> X<-A> X<-C>