INSTALL.rst : Update kwant install instructions for latest python version

INSTALL.rst

@@ -91,8 +91,16 @@ Install instructions for Linux systems
 
    *Note*: 
 
+   - If ``kwant`` fails to install, cloning it first and installing the pulled code may work as it is more recent
+   .. code:: shell
+
+        $ source tkwantoperator/bin/activate
+        $ git clone https://gitlab.kwant-project.org/kwant/kwant.git
+        $ cd kwant
+        $ pip3 install .
+
    - To install updates in any of the git repositories, simply redo the pip install.
-   - Install may fail on linux systems with the latest python and pip version. If so, please retry with the extra ``--no-build-isolation`` argument to pip
+   - Install may fail on linux systems with the latest python (3.9+) and pip version. If so, please retry with the extra ``--no-build-isolation`` argument to pip