Add link to export clauses doc to sidebar

Author: odersky

docs/docs/reference/other-new-features/export.md

@@ -1,6 +1,6 @@
 ---
 layout: doc-page
-title: "Export"
+title: "Export Clauses"
 ---
 
 An export clause defines aliases for selected members of an object. Example:

docs/sidebar.yml

@@ -71,6 +71,8 @@ sidebar:
               url: docs/reference/other-new-features/trait-parameters.html
             - title: Creator Applications
               url: docs/reference/other-new-features/creator-applications.html
+            - title: Export Clauses
+              url: docs/reference/other-new-features/export.html"
             - title: Inlining by Rewriting
               url: docs/reference/other-new-features/inline.html
             - title: Meta Programming