add development install instructions

Author: ianhi

{{cookiecutter.github_project_name}}/README.md

@@ -27,3 +27,45 @@ the nbextension:
 ```bash
 jupyter nbextension enable --py [--sys-prefix|--user|--system] {{ cookiecutter.python_package_name  }}
 ```
+
+## Development Installation
+
+
+```bash
+# First install the python package. This will also build the JS packages.
+pip install -e ".[test, examples]"
+```
+
+When developing your extensions, you need to manually enable your extensions with the
+notebook / lab frontend. For lab, this is done by the command:
+
+```
+jupyter labextension install @jupyter-widgets/jupyterlab-manager --no-build
+jupyter labextension install .
+```
+
+For classic notebook, you can run:
+
+```
+jupyter nbextension install --sys-prefix --symlink --overwrite --py <your python package name>
+jupyter nbextension enable --sys-prefix --py <your python package name>
+```
+
+Note that the `--symlink` flag doesn't work on Windows, so you will here have to run
+the `install` command every time that you rebuild your extension. For certain installations
+you might also need another flag instead of `--sys-prefix`, but we won't cover the meaning
+of those flags here.
+
+### How to see your changes
+#### Typescript:
+To continuously monitor the project for changes and automatically trigger a rebuild, start Jupyter in watch mode:
+```bash
+jupyter lab --watch
+```
+And in a separate session, begin watching the source directory for changes:
+```bash
+npm run watch
+```
+
+#### Python:
+If you make a change to the python code then you will need to restart the notebook kernel to have it take effect.