docs: document github webhooks

doc/manual/src/SUMMARY.md

@@ -8,6 +8,7 @@
 - [Plugins](./plugins/README.md)
   - [Declarative Projects](./plugins/declarative-projects.md)
 - [Using the external API](api.md)
+- [Webhooks](webhooks.md)
 - [Monitoring Hydra](./monitoring/README.md)
 
 ## Developer's Guide

doc/manual/src/webhooks.md

@@ -0,0 +1,13 @@
+# Webhooks
+
+Hydra can be notified by github's webhook to trigger a new evaluation when a
+jobset has a github repo in its input.
+To set up a github webhook go to `https://github.com/<yourhandle>/<yourrepo>/settings` and in the `Webhooks` tab
+click on `Add webhook`.
+
+- In `Payload URL` fill in `https://<your-hydra-domain>/api/push-github`.
+- In `Content type` switch to `application/json`.
+- The `Secret` field can stay empty.
+- For `Which events would you like to trigger this webhook?` keep the default option for events on `Just the push event.`.
+
+Then add the hook with `Add webhook`.