updated sage installation method with pip

Added sage library installation instructions using pip. Installing sage in a python virtual environment can be troublesome as `sage` and `sagemath` libraries, not at all related to this sage, exist in PiPy.

README.md

@@ -394,6 +394,18 @@ in the Installation Guide.
     or JupyterLab installation, as described in [section
     "Launching SageMath"](https://doc.sagemath.org/html/en/installation/launching.html)
     in the installation manual.
+
+Alternative Installation using PiPy
+---------------
+
+You can find `sage` and `sagemath` pip packages but it is worth nothing that they are not at all realted to this `sage`. Indeed `pip install sage` installs `sage 0.0.0` which is literally an empty package. For installation of this `sage` you need to install `sagemath-standard`. First activate your python virtual environment and follow these steps:
+
+            $ python3 -m pip install sage_conf
+            $ ls $(sage-config SAGE_SPKG_WHEELS)
+            $ python3 -m pip install $(sage-config SAGE_SPKG_WHEELS)/*.whl 
+            $ python3 -m pip install sagemath-standard
+
+You need to install the `sage_conf`, a wheelhouse of various python packages. You can list the wheels using `ls $(sage-config SAGE_SPKG_WHEELS)`. After manual installation of these wheels you can install the sage library, `sagemath-standard`. 
 
 Troubleshooting
 ---------------