python: redirect pyenv to home

linux/workstation/python.markdown

@@ -51,3 +51,11 @@ ipython kernel install --name "opt-software-pyenv" --user
 ```
 
 This creates a custom configuration `~/.local/share/jupyter/kernels/opt-software-pyenv/kernel.json` in your home. Inside JupyterHub you should now be able to pick this kernel in the `Kernel -> Change kernel` menu.
+
+### Use pyenv to install custom Python versions
+
+If you want to install your own Python versions, watch out to either not source our environment, or to redirect the pyenv installation to a location, where you have write access (either the local scratch or your home folder).
+
+```
+PYENV_ROOT=$HOME pyenv install <version>
+```