Add a sample overview of the data flow.

30.contributing/frontmatter.yaml

+visible: false
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30.contributing/page.en.md

+---
+title: Contributing
+slug: contributing
+---
+
+## How it works
+
+- Flat files
+  - enhanced markdown for content
+  - YAML frontmatter for metadata
+- Continuous integration
+- Versioning using git
+
+
+## Data Flow
+
+```mermaid
+
+graph LR
+
+User(Teacher)
+Website[M3P2 Website]
+Local[Local Website]
+Git[Git]
+GitLab[GitLab]
+
+User --> |contributes via| Git
+User --> |contributes via| GitLab
+User --> |contributes via| Local
+
+Local --> |triggers| Git
+Git --> |triggers| GitLab
+GitLab --> |updates| Website
+
+```
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