doc: add recommendations for first timers

PR-URL: #16350
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>

COLLABORATOR_GUIDE.md

@@ -24,8 +24,9 @@ understand the project governance model as outlined in
 
 ## Issues and Pull Requests
 
-Courtesy should always be shown to individuals submitting issues and
-pull requests to the Node.js project.
+Courtesy should **always** be shown to individuals submitting issues and pull
+requests to the Node.js project. Be welcoming to first time contributors,
+identified by the GitHub ![badge](./doc/first_timer_badge.png) badge.
 
 Collaborators should feel free to take full responsibility for
 managing issues and pull requests they feel qualified to handle, as
@@ -68,6 +69,9 @@ wide-reaching impact), and focused changes that affect only documentation
 and/or the test suite, may be landed after a shorter delay if they have
 multiple approvals.
 
+For first time contributors, ask the author if they have configured their git
+username and email to their liking as per [this guide][git-username].
+
 For non-breaking changes, if there is no disagreement amongst
 Collaborators, a pull request may be landed given appropriate review.
 Where there is discussion amongst Collaborators, consensus should be
@@ -356,10 +360,8 @@ The TSC should serve as the final arbiter where required.
   * If you do, please force-push removing the merge.
   * Reasons for not using the web interface button:
     * The merge method will add an unnecessary merge commit.
-    * The rebase & merge method adds metadata to the commit title.
-    * The rebase method changes the author.
     * The squash & merge method has been known to add metadata to the
-    commit title.
+    commit title (the PR #).
     * If more than one author has contributed to the PR, keep the most recent
       author when squashing.
 
@@ -669,3 +671,4 @@ LTS working group and the Release team.
 [backporting guide]: doc/guides/backporting-to-release-lines.md
 [Stability Index]: doc/api/documentation.md#stability-index
 [Enhancement Proposal]: https://github.com/nodejs/node-eps
+[git-username]: https://help.github.com/articles/setting-your-username-in-git/