doc: add CI help/support info to onboarding doc

PR-URL: #8407
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/onboarding.md

@@ -115,6 +115,10 @@ onboarding session.
       * The `CERTIFY_SAFE` box should be checked. By checking it, you are indicating that you have reviewed the code you are about to test and you are confident that it does not contain any malicious code. (We don't want people hijacking our CI hosts to attack other hosts on the internet, for example!)
       * The `PR_ID` box should be filled in with the number identifying the pull request containing the code you wish to test. For example, if the URL for the pull request is `https://github.com/nodejs/node/issues/7006`, then put `7006` in the `PR_ID`.
       * The remaining elements on the form are typically unchanged with the exception of `POST_STATUS_TO_PR`. Check that if you want a CI status indicator to be automatically inserted into the PR.
+    * If you need help with something CI-related:
+      * Use #node-dev (IRC) to talk to other Collaborators.
+      * Use #node-build (IRC) to talk to the Build WG members who maintain the CI infrastructure.
+      * Use the [Build WG repo](https://github.com/nodejs/build) to file issues for the Build WG members who maintain the CI infrastructure.
 
 
 ## Landing PRs: Overview