Docs: Contribution guidelines for updating Drone pipelines (#69530)

* Create drone-pipeline.md

* Update drone-pipeline.md

* Update README.md

* Update drone-pipeline.md

* Apply suggestions from code review

Co-authored-by: Horst Gutmann <horst.gutmann@grafana.com>

* Format file

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Co-authored-by: Horst Gutmann <horst.gutmann@grafana.com>

contribute/README.md

@@ -7,6 +7,7 @@ This directory contains guides for contributors to the Grafana project.
 - [Developer guide](developer-guide.md)
 - [Triage issues](triage-issues.md)
 - [Merge a pull request](merge-pull-request.md)
+- [Making changes to the CI pipeline](drone-pipeline.md)
 
 The `style-guides` directory contains style guides for the Grafana software project and documentation.
 

contribute/drone-pipeline.md

@@ -0,0 +1,17 @@
+# Making changes to the Drone pipeline
+
+_Only people in the Grafana organization can make changes to the Drone pipeline_
+
+The Drone pipelines are built with [Starlark](https://github.com/bazelbuild/starlark), a language which is similar to Python. The Starlark files are located in [`scripts/drone`](https://github.com/grafana/grafana/tree/main/scripts/drone).
+
+## Setup
+
+- Set environment variables `DRONE_SERVER` and `DRONE_TOKEN`, which can be found on your [Drone account](https://drone.grafana.net/account). These are used to verify that only Grafana employees can make changes to the pipelines.
+- Install [buildifier](https://github.com/bazelbuild/buildtools/blob/master/buildifier/README.md), and use it to format the Starlark files you edit.
+
+## Develop
+
+- Open a PR where you can do test runs for your changes. If you need to experiment with secrets, create a PR in the [grafana-ci-sandbox repo](https://github.com/grafana/grafana-ci-sandbox), before opening a PR in the main repo.
+- Run `make drone` after making changes to the Starlark files. This builds the `.drone.yml` file.
+
+For further questions, reach out to the grafana-delivery squad.