Point out sub EXPORT must be before unit

https://irclog.perlgeek.de/perl6/2018-05-23#i_16195729

doc/Language/modules.pod6

@@ -410,6 +410,18 @@ Then use the tag you like and pick the symbol by its name.
     # OUTPUT: «(&uri-escape &uri-unescape &uri_escape &uri_unescape)␤»
     my &escape-uri = URI::Escape::EXPORT::DEFAULT::<&uri_escape>;
 
+Be careful I<not> to put C<sub EXPORT> after L«C<unit> declarator|/syntax/unit».
+If you do so, it'll become just a sub inside your package, rather than the special
+export sub:
+
+    unit module Bar;
+    sub EXPORT { %(Foo => &say) } # WRONG!!! Sub is scoped wrong
+    
+    # ---------
+    
+    sub EXPORT { %(Foo => &say) } # RIGHT!!! Sub is outside the module
+    unit module Bar;
+
 =head2 Finding Modules
 
 It is up to the module installer to know where C<compunit> expects modules to