mention correct usage of export in the manual, fixes #6227 [ci skip]

doc/manual.rst

@@ -6653,6 +6653,13 @@ modules don't need to import a module's dependencies:
 When the exported symbol is another module, all of its definitions will
 be forwarded. You can use an ``except`` list to exclude some of the symbols.
 
+Notice that when exporting, you need to specify only the module name:
+
+.. code-block:: nim
+  import foo/bar/baz
+  export baz
+
+
 
 Scope rules
 -----------