docs: add explanation and link to job.

Co-authored-by: Justin M. Keyes <[email protected]>

Author: Hweinstock

.github/workflows/node.js.yml

@@ -87,6 +87,8 @@ jobs:
             - name: Merge in target branch to avoid false negatives.
               env:
                   TARGET_BRANCH: ${{ github.event.pull_request.base.ref }}
+              # Note: "git merge" should always succeed here, because GHA won't
+              # start the job if there are merge conflicts. https://github.com/orgs/community/discussions/11265
               run: |
                   git merge origin/$TARGET_BRANCH