Update installation (#14732)

* Update installation

Updates to use python -m pip install -U lightning and adds troubleshooting note

* Apply suggestions from code review

Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>

docs/source-app/index.rst

@@ -27,7 +27,7 @@ Install Lightning
 
 .. code-block:: bash
 
-   pip install lightning
+   python -m pip install -U lightning
 
 
 Or read the :ref:`advanced install <install>` guide.

docs/source-app/installation.rst

@@ -28,3 +28,11 @@ Install with pip
     .. code:: bash
 
         python -m pip install -U lightning
+
+.. note::
+
+    If you encounter issues during installation use the following to help troubleshoot:
+
+	.. code:: bash
+
+            pip list | grep lightning

docs/source-app/installation_mac.rst

@@ -19,4 +19,4 @@ Install the ``lightning`` package
         export GRPC_PYTHON_BUILD_SYSTEM_OPENSSL=1
         export GRPC_PYTHON_BUILD_SYSTEM_ZLIB=1
 
-        pip install lightning
+        python -m pip install -U lightning