Added #! to nanovna-saver, updated README

There was a question on the nanovna list showing confusion about which
file was indended to be the executable.  This commit makes three small
changes to ease that issue.

* it updates the README with a run instruction
* it grants nanovna-saver.py executable permission
* it adds '#! /bin/env python' to the start of nanovna-saver.py so it is
directly executable.

README.md

@@ -34,6 +34,12 @@ In order to run this app in Linux environment, you'll need the following package
 * `python3-serial`
 * `python3-pyqt5`
 
+### To Run
+
+```sh
+python3 nanovna-saver.py
+```
+
 ### License
 This software is licensed under version 3 of the GNU General Public License. It comes with NO WARRANTY.
 

nanovna-saver.py

@@ -1,3 +1,5 @@
+#! /bin/env python
+
 #  NanoVNASaver - a python program to view and export Touchstone data from a NanoVNA
 #  Copyright (C) 2019.  Rune B. Broberg
 #