DOC fix the path of html files in contributing.md (scikit-learn#10688)

CONTRIBUTING.md

@@ -217,7 +217,7 @@ You can edit the documentation using any text editor and then generate
 the HTML output by typing ``make html`` from the doc/ directory.
 Alternatively, ``make`` can be used to quickly generate the
 documentation without the example gallery. The resulting HTML files will
-be placed in ``_build/html/`` and are viewable in a web browser. See the
+be placed in ``_build/html/stable`` and are viewable in a web browser. See the
 ``README`` file in the ``doc/`` directory for more information.
 
 For building the documentation, you will need