Add Open VSX member page

Resolves #41 (closed)

DO NOT MERGE until the members page exists on production.

src/main/resources/working_groups.json

@@ -743,7 +743,7 @@
               }
           },
           "website": "",
-          "members": "",
+          "members": "https://open-vsx.org/members",
           "sponsorship": "https://www.eclipse.org/org/workinggroups/sponsorship/working-group-sponsorship-agreement.pdf",
           "contact_form": "https://accounts.eclipse.org/contact/membership"
       },