Explain the automated deployment processes

* make it clear that Hugo/the template distinguishes content types based on frontmatter fields
* explain what the key differences are
* link to the archetypes so people can better understand what the relevant fields are

Reviewed-on: #165
Reviewed-by: jtbx <jtbx@noreply.git.hamburg.ccc.de>

README.md

@@ -30,6 +30,7 @@ Running the hugo command without and parameters will re-generate the site in the
 To deploy the website, just copy the whole folder to a directory which is servered by the webserver of your preference.
 
 Please note that the website should be re-deployed at least daily to update the "announcement" section on the front page even if there were no changed to the content.
+See [Automated Deployment](#automated-deployment) for the way the deployment is set up on git.hamburg.ccc.de
 
 ### Previewing Changes Locally
 
@@ -119,6 +120,19 @@ If you have set a `publishDate` to a date and time in the future, the preview wi
 Once at least one reviewer approves the PR, it will be merged and pushed to production.
 This usually takes less than five minutes.
 
+### Automated Deployment
+
+The website is automatically rebuilt and redeployed every 20 minutes. At each build and deploy:
+* The event calendar is fetched.
+* Hugo renders all pages.
+* All changed files are deployed to the production web server.
+
+See [.forgejo/workflows/deploy.yaml](.forgejo/workflows/deploy.yaml) for all the details.
+
+Additionally, for each pull request, a version of the website is deployed to the staging website under a unique URL.
+The pull request will be updated with the URL, so you and the reviewers can look at the changes as they will appear after merging.
+After the PR is closed, the URL will be removed.
+
 #### Populate the Event Calendar
 
 The event calendar table is filled from the Nextcloud iCal feed.