Add docs for 3.0 (#4705)

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Co-authored-by: qwerty287 <qwerty287@posteo.de>
Co-authored-by: Robert Kaussow <mail@thegeeklab.de>
Co-authored-by: Anbraten <anton@ju60.de>
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docs/versioned_docs/version-3.0/20-usage/10-intro.md

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+# Your first pipeline
+
+Let's get started and create your first pipeline.
+
+## 1. Repository Activation
+
+To activate your repository in Woodpecker navigate to the repository list and `New repository`. You will see a list of repositories from your forge (GitHub, Gitlab, ...) which can be activated with a simple click.
+
+![new repository list](repo-new.png)
+
+To enable a repository in Woodpecker you must have `Admin` rights on that repository, so that Woodpecker can add something
+that is called a webhook (Woodpecker needs it to know about actions like pushes, pull requests, tags, etc.).
+
+## 2. Define first workflow
+
+After enabling a repository Woodpecker will listen for changes in your repository. When a change is detected, Woodpecker will check for a pipeline configuration. So let's create a file at `.woodpecker/my-first-workflow.yaml` inside your repository:
+
+```yaml title=".woodpecker/my-first-workflow.yaml"
+when:
+  - event: push
+    branch: main
+
+steps:
+  - name: build
+    image: debian
+    commands:
+      - echo "This is the build step"
+      - echo "binary-data-123" > executable
+  - name: a-test-step
+    image: golang:1.16
+    commands:
+      - echo "Testing ..."
+      - ./executable
+```
+
+**So what did we do here?**
+
+1. We defined your first workflow file `my-first-workflow.yaml`.
+2. This workflow will be executed when a push event happens on the `main` branch,
+   because we added a filter using the `when` section:
+
+   ```diff
+   + when:
+   +   - event: push
+   +     branch: main
+
+   ...
+   ```
+
+3. We defined two steps: `build` and `a-test-step`
+
+The steps are executed in the order they are defined, so `build` will be executed first and then `a-test-step`.
+
+In the `build` step we use the `debian` image and build a "binary file" called `executable`.
+
+In the `a-test-step` we use the `golang:1.16` image and run the `executable` file to test it.
+
+You can use any image from registries like the [Docker Hub](https://hub.docker.com/search?type=image) you have access to:
+
+```diff
+ steps:
+   - name: build
+-    image: debian
++    image: my-company/image-with-aws_cli
+     commands:
+       - aws help
+```
+
+## 3. Push the file and trigger first pipeline
+
+If you push this file to your repository now, Woodpecker will already execute your first pipeline.
+
+You can check the pipeline execution in the Woodpecker UI by navigating to the `Pipelines` section of your repository.
+
+![pipeline view](./pipeline.png)
+
+As you probably noticed, there is another step in called `clone` which is executed before your steps. This step clones your repository into a folder called `workspace` which is available throughout all steps.
+
+This for example allows the first step to build your application using your source code and as the second step will receive
+the same workspace it can use the previously built binary and test it.
+
+## 4. Use a plugin for reusable tasks
+
+Sometimes you have some tasks that you need to do in every project. For example, deploying to Kubernetes or sending a Slack message. Therefore you can use one of the [official and community plugins](/plugins) or simply [create your own](./51-plugins/20-creating-plugins.md).
+
+If you want to get a Slack notification after your pipeline has finished, you can add a Slack plugin to your pipeline:
+
+```yaml
+steps:
+  # ...
+  - name: notify me on Slack
+    image: plugins/slack
+    settings:
+      channel: developers
+      username: woodpecker
+      password:
+        from_secret: slack_token
+    when:
+      status: [success, failure] # This will execute the step on success and failure
+```
+
+To configure a plugin you can use the `settings` section.
+
+Sometime you need to provide secrets to the plugin. You can do this by using the `from_secret` key. The secret must be defined in the Woodpecker UI. You can find more information about secrets [here](./40-secrets.md).
+
+Similar to the `when` section at the top of the file which is for the complete workflow, you can use the `when` section for each step to define when a step should be executed.
+
+Learn more about [plugins](./51-plugins/51-overview.md).
+
+As you now have a basic understanding of how to create a pipeline, you can dive deeper into the [workflow syntax](./20-workflow-syntax.md) and [plugins](./51-plugins/51-overview.md).