Update webhook-api docs

chat/matrix/bridges.markdown

@@ -70,9 +70,13 @@ Base URL: `https://webhooks.mbot.ethz.ch/webhook/grafana/<hook>`
 3. Paste the url into the **Url** field
 4. Disable **Notification settings** > **Include image**
 
-### Grafana Slack notification (deprecated)
+Optional: Select another notification template using a query parameter: `?template=<template>`.
+Refer to the [configuration section](https://gitlab.ethz.ch/isgphys/webhook-to-matrix-hookshot#configuration)
+for details.
 
-**Do not use.** Use Grafana webhook notification instead.
+### Grafana Slack notification (deprecated for Grafana)
+
+**Do not use for Grafana alerts.** Use Grafana webhook notification instead.
 
 Base URL: `https://webhooks.mbot.ethz.ch/webhook/slack/<hook>`