docs: clarify staging

Specify that the merges from master to staging-next to staging are
performed by GitHub actions. This helps the reader understand the
relationship between the branches.

1 files changed, 4 insertions, 1 deletions

diff --git a/doc/contributing/submitting-changes.chapter.md b/doc/contributing/submitting-changes.chapter.md
index 40fc5ea7892..44e981f12a5 100644
--- a/doc/contributing/submitting-changes.chapter.md
+++ b/doc/contributing/submitting-changes.chapter.md
@@ -174,10 +174,13 @@ digraph {
     "staging-next" -> master [color="#E85EB0"] [label="stabilization ends"] [fontcolor="#E85EB0"]
     "staging" -> "staging-next" [color="#E85EB0"] [label="stabilization starts"] [fontcolor="#E85EB0"]
 
-    master -> "staging-next" -> staging [color="#5F5EE8"] [label="every six hours/any time"] [fontcolor="#5F5EE8"]
+    master -> "staging-next" -> staging [color="#5F5EE8"] [label="every six hours (GitHub Action)"] [fontcolor="#5F5EE8"]
 }
 ```
 
+[This GitHub Action](https://github.com/NixOS/nixpkgs/blob/master/.github/workflows/merge-staging.yml) brings changes from `master` to `staging-next` and from `staging-next` to `staging` every 6 hours.
+
+
 ### Master branch {#submitting-changes-master-branch}
 
 The `master` branch is the main development branch. It should only see non-breaking commits that do not cause mass rebuilds.