doc: instructions on how to make membership public

PR-URL: #17688
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Author: mhdawson

doc/onboarding.md

@@ -38,6 +38,10 @@ onboarding session.
       * Branches in the nodejs/node repository are only for release lines
     * [See "Updating Node.js from Upstream"](./onboarding-extras.md#updating-nodejs-from-upstream)
     * Make a new branch for each PR you submit.
+    * Membership: Consider making your membership in the Node.js GitHub organization
+      public. This makes it easier to identify Collaborators. Instructions on how to
+      do that are available at
+      [Publicizing or hiding organization membership](https://help.github.com/articles/publicizing-or-hiding-organization-membership/).
 
   * Notifications:
     * Use [https://github.com/notifications](https://github.com/notifications) or set up email