Add python extractor

README.md

@@ -8,6 +8,37 @@ Follow the guide over [here](https://docs.cypress.io/guides/getting-started/inst
 
 You also require NodeJS. Run `npm ci` to install the required packages.
 
+Create new python venv:
+```
+python -m venv venv
+```
+
+Activate the new environment (linux)
+
+```
+source venv/bin/activate
+```
+
+Install the requirements
+```
+pip -r requirements.txt
+```
+
 ## Execution
 
 To start cypress, simply execute `npx cypress open`. Then click `E2E Testing` and run using electron. This step could be automated using the `cypress` [API](https://docs.cypress.io/guides/guides/module-api).
+
+Start the extractor
+```
+python hedgedoc-image.py meta_pad new_netloc
+```
+
+For example:
+```
+python hedgedoc-image.py https://md.margau.net/dbk-meta pad.hacknang.de
+```
+
+## Produced files
+
+The python scripts produces a `pads.json` which contains the mapping from `old_url` to `new_url`.
+All images land in `images/uploads`. Only images hosted on the `old_pads` URL are saved