Add basic readme

README.md

+# 37C3 info pages
+
+This repository contains the source code for the 37C3 info pages. The pages are
+available at https://events.ccc.de/congress/2023/infos/.
+
+## Development
+
+The pages are built using [mkdocs](https://www.mkdocs.org/). To install it, install mkdocs using pip,
+ideally in a virtual environment:
+
+```bash
+pip install -r requirements.txt
+```
+
+Then, to start a local development server, run:
+
+```bash
+mkdocs serve
+```