Add Documentation for integrating with Read the Docs (#289)

This adds a Documentation for connecting Codeberg to [Read the Docs](https://readthedocs.org/). English is not my native Language, so there may be a few things that could be written better.

Co-authored-by: René Wagner <rwa@clttr.info>
Reviewed-on: https://codeberg.org/Codeberg/Documentation/pulls/289
Co-authored-by: JakobDev <jakobdev@gmx.de>
Co-committed-by: JakobDev <jakobdev@gmx.de>

content/integrations/read-the-docs.md

@@ -0,0 +1,82 @@
+---
+eleventyNavigation:
+  key: Read the Docs Integration
+  title: Integrating with Read the Docs
+  parent: Integrations
+---
+
+This article will guide you through integrating Codeberg with [Read the Docs](https://readthedocs.org/) to allow automatic build of your documentation. It will show you how to connect Read the Docs to a Git repository hosted on Codeberg. To learn how Read the Docs works, take a look at the [official Documentation](https://docs.readthedocs.io).
+
+> Gitea/Forgejo is currenly not official supported by Read the Docs, so this may break in the future.
+
+## Registration
+
+If you do not have an account yet, you must sign up with [readthedocs first](https://readthedocs.org/accounts/signup/).
+
+After sign-up you need to login with your user to access your [dashboard](https://readthedocs.org/dashboard/).
+
+## Create new Project
+This steps shows how to create a new project on Read the Docs
+
+1. On the [Read the Docs dashboard](https://readthedocs.org/dashboard/) click "Import a Project"
+2. If you have connected Read the Docs with some provider e.g. GitHub, you see a list of your repos at that provider. Ignore it and click "Import Manually". You should see this screen:
+   
+<picture>
+  <source srcset="/assets/images/integrations/read-the-docs/import-manual.webp" type="image/webp">
+  <img src="/assets/images/integrations/read-the-docs/import-manual.png" alt="Image of the Import Manual page">
+</picture>
+
+1. Under "Name" enter the name of your project. Under "Repository URL" enter the Git URL of your repo. It has the form `https://codeberg.org/<owner>/<repo>.git`. Leave the rest as it is and click "Next"
+2. You should now be on your Project page and see a warning that the project doesn't have a valid Webhook. Ignore that. Go to Admin->Integrations. You should see this screen:
+
+<picture>
+  <source srcset="/assets/images/integrations/read-the-docs/admin-integrations.webp" type="image/webp">
+  <img src="/assets/images/integrations/read-the-docs/admin-integrations.png" alt="Image of an admin website of a Read the docs project.
+  The integrations section of the admin page is selected.
+  The content of the Integrations sections states, that 'No integrations are currently configured.'.
+  An error message is shown in red saying that the project does not have a valid webhook set up.">
+</picture>
+
+5. Now click on "Add Integration" and select "GitHub incoming webhook" as type. You should see this screen:
+
+<picture>
+  <source srcset="/assets/images/integrations/read-the-docs/github-integration.webp" type="image/webp">
+  <img src="/assets/images/integrations/read-the-docs/github-integration.png" alt="Image of an admin website of a Read the docs project.
+  The integrations section of the admin page is selected.
+  The page content start with a header saying 'Integration - GitHub incoming webhook'.
+  After some explaining text an url specific to the Read the docs project is shown which can be used to manually configure this webhook.
+  The url shown is marked with a red border.">
+</picture>
+
+6. Copy the URL that is marked Red in the Image. You should keep it secret, as it allows pushing to your Documentation
+7. Now go to the "Webhooks" Section of the settings of your Codeberg Repo. Create a new "Forgejo" Webhook
+
+<picture>
+  <source srcset="/assets/images/integrations/read-the-docs/forgejo-webhook.webp" type="image/webp">
+  <img src="/assets/images/integrations/read-the-docs/forgejo-webhook.png" alt="Image of a Forgejo repository configuration.
+  The tab 'Webhooks' is selected.
+  The button 'Add Webhook' has been clicked and presents a list of possible Webhooks integrations.
+  The 'Forgejo' entry in the list has been marked with a red border.">
+</picture>
+ 
+8. Under "Target URL" enter the URL you copied from the Read the Docs webhook
+9. Under "Trigger On:" select "All Events"
+
+<picture>
+  <source srcset="/assets/images/integrations/read-the-docs/add-webhook.webp" type="image/webp">
+  <img src="/assets/images/integrations/read-the-docs/add-webhook.png" alt="Image of the Forgejo 'Add Webhook' dialog. 
+  The input field for 'Target URL' is marked with a red border. 
+  Also the 'All Events' checkout below the 'Trigger On' section is marked with a red border.">
+</picture>
+
+Congratulation! Your done! To test it, push a commit in your Codeberg Repo and see if the documentation rebuilds. This may take a few minutes.
+
+## Migrate Project
+You may migrate a repo that is connected to Read the Docs from another git forge to Codeberg. In this case, follow these steps:
+
+1. Go to Admin->Settings of your Project on Read the Docs
+2. Under "Repository URL" enter the Git URL of your Codeberg Repo
+3. Now go to "Integrations". You will see a existing Integration
+4. Click on it to open the Settings of the Integration
+5. Now click on "Delete Webhook"
+6. Jump to Step 5 of the "Create new project" section and follow the steps there