docs: enhance installation instructions and improve backward compatibility

Author: tomondre

README.md

@@ -20,12 +20,12 @@ Reana JupyterLab plugin provides a set of tools to interact with the [Reana](htt
 ## Installation guide for users
 To install the extension, run the following command:
 ```bash
-pip install reana-jupyterlab
+python -m pip install reana-jupyterlab
 ```
 
 In case you want to run the tests, install the extension with the following command:
 ```bash
-pip install reana-jupyterlab[dev]
+python -m pip install reana-jupyterlab[dev]
 ```
 
 ### Docker image
@@ -52,17 +52,18 @@ Build the extension
 jlpm run build
 ```
 
-Install the extension (including the testing dependencies)
+Install the extension in editable mode and include the development dependencies:
 ```bash
-python -m pip install .[dev]
+python -m pip install -e .
+python -m pip install ".[dev]"
 ```
 
 Enable the server extension
 ```bash
-jupyter server extension enable --py reana_jupyterlab
+python -m jupyter server extension enable --py reana_jupyterlab.server
 ```
 
 Finally, open a JupyterLab instance. The extension should be available in the JupyterLab sidebar.
 ```bash
-jupyter lab
-```
+python -m jupyter lab
+```

reana_jupyterlab/__init__.py

@@ -18,4 +18,11 @@ def _jupyter_labextension_paths():
 def _jupyter_server_extension_points():  # pragma: no cover
     return [{
         "module": "reana_jupyterlab.server"
-    }]
+    }]
+
+# Import and expose the server extension loading function for backward compatibility
+# Fixes `X Validation failed: validation failed` error
+
+from .server import _load_jupyter_server_extension
+
+load_jupyter_server_extension = _load_jupyter_server_extension