use higher-quality logo, svg file in README

README.md

@@ -1,6 +1,6 @@
 # FASTSim
 
-![FASTSim Logo](https://www.nrel.gov/transportation/assets/images/icon-fastsim.jpg)
+<img src="docs/assets/fastsim-icon.svg" height="200">
 
 [![homepage](https://img.shields.io/badge/homepage-fastsim-blue)](https://www.nrel.gov/transportation/fastsim.html) [![tests](https://github.com/NREL/fastsim/actions/workflows/tests.yaml/badge.svg)](https://github.com/NREL/fastsim/actions/workflows/tests.yaml) [![wheels](https://github.com/NREL/fastsim/actions/workflows/wheels.yaml/badge.svg)](https://github.com/NREL/fastsim/actions/workflows/wheels.yaml?event=release) [![python](https://img.shields.io/badge/python-3.8%20%7C%203.9%20%7C%203.10-blue)](https://pypi.org/project/fastsim/) [![documentation](https://img.shields.io/badge/documentation-book-blue.svg)](https://nrel.github.io/fastsim/) [![github](https://img.shields.io/badge/github-fastsim-blue.svg)](https://github.com/NREL/fastsim)