Add usage instructions

README.md

+# CodiMD note exporter
+
+This little tool is intended to help you backup the notes that you have in your CodiMD history to a
+local folder. It complements CodiMD's "export user data" functionality, which only downloads
+documents that you own.
+
+## Requirements
+
+Its only dependency is Python >= 3.7 (use `python3 -V` to check your version).
+
+## Usage
+
+### 1. Extract value of the session cookie
+
+First of all, you need to extract the value of the `connect.sid` browser cookie for the
+particular CodiMD instance that you use (e.g., `md.inf.tu-dresden.de`).
+
+**WARNING**: the value of the cookie is your session ID and as such, **should be treated like a
+password**. Don't share it with others!
+
+Now, the instructions are similar for Chrome and Firefox:
+
+1. Navigate to the CodiMD instance.
+2. Open developer tools.
+3. **Chrome**: go to the "Application" tab. **Firefox**: go to the "Storage" tab ("Web-Speicher").
+4. Un-collapse "Cookies".
+5. In the list, search for a cookie with the name `connect.sid`
+6. Select and copy the value.
+
+
+### 2. Execute the script via the command line
+
+Clone this repository to a path of your liking and just execute `./codimd_export.py` in a
+shell. The script will ask for your session id and download the notes to the relative path
+`./codimd-documents`.
+
+
+### Example
+
+    $️ ./codimd_export.py
+    Please provide your CodiMD session id (connect.sid cookie):
+    HTTP 404 Not Found: https://md.inf.tu-dresden.de/TOPofLSB
+    HTTP 404 Not Found: https://md.inf.tu-dresden.de/6jeKGnJnSp6H0f0mVnBwQQ
+    HTTP 403 Forbidden: https://md.inf.tu-dresden.de/klausur-2020-experiences
+    HTTP 404 Not Found: https://md.inf.tu-dresden.de/iQVB7TO-QXqi3hGSZ7J4Eg
+    HTTP 404 Not Found: https://md.inf.tu-dresden.de/LSB-2020-11-17
+    HTTP 404 Not Found: https://md.inf.tu-dresden.de/Nzbj13ydRLe1d0fRCyG6cA
+    HTTP 404 Not Found: https://md.inf.tu-dresden.de/LSB-2021-02-02
+    HTTP 404 Not Found: https://md.inf.tu-dresden.de/LSB-2021-06-22
+    HTTP 404 Not Found: https://md.inf.tu-dresden.de/LSB-2021-12-07
+    HTTP 404 Not Found: https://md.inf.tu-dresden.de/ThesisTemplateBachelor
+    HTTP 404 Not Found: https://md.inf.tu-dresden.de/cnoGl7hoTaK1JIh2-u-h0g
+    Done: 163 notes successfully downloaded, 11 not accessible.