doc: use full URL for package index, now build separately

documentation/source/index.rst

@@ -95,16 +95,12 @@ articles, and all the library docs.
    Dylan Programming Guide <https://opendylan.org/books/dpg/>
    Dylan Playground <https://play.opendylan.org>
 
-.. Note that the package/index reference below is not part of this
-   repository; it's generated by the gendoc library, which (obviously)
-   must be run before `make html`.
-
 .. toctree::
    :caption: Reference
    :hidden:
 
    Dylan Reference Manual <https://opendylan.org/books/drm/>
-   Package Docs <package/index>
+   Package Docs <https://opendylan.org/package/>
    Open Dylan Libraries <library-reference/index>
    All Documentation <documentation/index>
    Full Index <genindex>