docs: update readme, jupyterlab 3 is now required

Author: consideRatio

labextension/README.md

@@ -7,11 +7,11 @@ configured server processes managed by the python package `jupyter-server-proxy`
 
 ## Prerequisites
 
-- JupyterLab >=2,<5
+- JupyterLab >=3,<5
 
 ## Installation
 
-For JupyterLab 3+, use your preferred Python package manager to install `jupyter-server-proxy`:
+Use your preferred Python package manager to install `jupyter-server-proxy`:
 
 ```bash
 pip install jupyter-server-proxy
@@ -26,18 +26,3 @@ conda install jupyter-server-proxy
 > As a _prebuilt_ extension, it will "just work," only a simple page reload should be required
 > to see launcher items. However, a full restart of `jupyter_server` or `notebook` is required
 > to reload the `jupyter_server_proxy` serverextension which provides most of the functionality.
-
-### JupyterLab 2
-
-For JupyterLab 2, ensure `nodejs` is installed and available on `$PATH` and run:
-
-```bash
-jupyter labextension install @jupyterhub/jupyter-server-proxy
-```
-
-> This will cause:
->
-> - a download of a great deal of build assets from `npmjs.org`
-> - a large `webpack` build that may exhaust memory and open files handles
->
-> **Please** consider upgrading to JupyterLab 3+ before reporting issues.