Update DISCLAIMER.md

doc/DISCLAIMER.md

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+## Updating configuration files
+
+Install the new version of the app with:
+
+```bash
+sudo yunohost app install https://github.com/YunoHost-Apps/jupyterlab_ynh/tree/testing  
+```
+
+Navigate to the installation path (`/opt/jupyterlab` by default), and run :
+
+```bash
+pipenv shell
+```
+
+You are now in the virtual environment of jupyterlab. You can execute these two commands:
+
+- To generate the `jupyterhub_config.py` file:
+
+```bash
+jupyterhub --generate-config
+```
+
+- To generate the `jupyter_notebook_config.py` file:
+
+```bash
+jupyter notebook --generate-config
+cp $HOME/.jupyter/jupyter_notebook_config.py ./
+```
+
+You can now update the old template files with the new one.