Update DEVELOPER.md

DEVELOPER.md

+# Developer Information
+
+## General overview
+
+This Jupyter extension contains of two components:
+
+* **Jupyter serverextension**
+   * written in Python
+   * see [jupyter-openbis-extension/](jupyter-openbis-extension)
+   * is registered with the `jupyter serverextension enable --py jupyter-openbis-extension` command
+   * registration should happen automatically when installilng via `pip install jupyter-openbis-extension`
+   * this serverextension is loaded whenever a Jupyter server is started – either `jupyter notebook` or `jupyter lab`
+   * serverextension talks to openBIS instances via the [pyBIS module](https://pypi.org/project/PyBIS/)
+   * serverextension also talks to the notebook extension (see below) via https
+   * serverextension uses an instance of the [tornado webserver](https://www.tornadoweb.org/en/stable/) that is used by Jupyter
+   * downloads and uploads dataSets and openBIS metadata
+
+* **Jupyter notebook extension** (aka Jupyter nbextension)
+   * written in JavaScript
+   * see [jupyter-openbis-extension/static](jupyter-openbis-extension/static)
+   * is registered with the `jupyter nbextension install --py jupyter-openbis-extension --user` and `jupyter nbextension enable --py jupyter-openbis-extension --user` commands
+   * registration should happen automatically when installilng via `pip install jupyter-openbis-extension`
+   * nbextension is started whenever a notebook is opened
+   * a new instance of the nbextension is started for *every* notebook
+   * displays the three prominent buttons (configuration, download, upload) inside a Jupyter notebook
+   * talks to the Jupyter serverextension (see above) via https requests
+
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