Add more information in README

Also allow triggering manual runs.

.github/workflows/kernels.yml

@@ -6,7 +6,8 @@
 name: Kernels
 
 on:
-  push:
+  workflow_dispatch:        # Manual trigger
+  push:                     # Automatic trigger
     branches: [ "master" ]
 
 concurrency:

README.md

@@ -1,3 +1,31 @@
 # kernels
 
 This repository holds both infrastructure and assets for bpftrace's CI kernels.
+
+We use a [dummy release][1] as an object store.
+
+## Adding a new kernel
+
+To add a new kernel, update [KERNELS][0] with the upstream tag of the version
+you want. Examples:
+
+* `v6.12`
+* `v6.12-rc7`
+
+Once the change is checked in, automation will build and upload any kernels not
+already present in the [Assets Release][1] to the assets release.
+
+## Changing already-built kernels
+
+Automation is not yet smart enough to rebuild and reupload existing assets
+affected by a config or infra change. If you want to change an already-uploaded
+kernel, delete the impacted kernel from the release assets and trigger a new
+run.
+
+You can trigger a new run by going to [the workflow page][2] and following
+[these docs][3] to trigger a manual run.
+
+[0]: ./KERNELS
+[1]: https://github.com/bpftrace/kernels/releases/tag/assets
+[2]: https://github.com/bpftrace/kernels/actions/workflows/kernels.yml
+[3]: https://docs.github.com/en/actions/managing-workflow-runs-and-deployments/managing-workflow-runs/manually-running-a-workflow