Adjust README badges and use Public Domain license badge

Author: ChrisChilders-USDA

README.md

@@ -4,11 +4,9 @@
 [![codecov](https://codecov.io/gh/NAL-i5K/GFF3toolkit/graph/badge.svg)](https://codecov.io/gh/NAL-i5K/GFF3toolkit)
 [![PyPI version](https://badge.fury.io/py/gff3tool.svg)](https://badge.fury.io/py/gff3tool)
 [![PyPI - Python Version](https://img.shields.io/pypi/pyversions/gff3tool)](https://pypi.org/project/gff3tool/)
-[![License](https://img.shields.io/github/license/NAL-i5K/GFF3toolkit)](https://github.com/NAL-i5K/GFF3toolkit/blob/master/LICENSE.md)
+[![License: Public Domain](https://img.shields.io/badge/license-Public%20Domain-blue.svg)](https://github.com/NAL-i5K/GFF3toolkit/blob/master/LICENSE.md)
 [![PyPI Downloads](https://img.shields.io/pypi/dm/gff3tool)](https://pypi.org/project/gff3tool/)
 [![GitHub release](https://img.shields.io/github/v/release/NAL-i5K/GFF3toolkit)](https://github.com/NAL-i5K/GFF3toolkit/releases)
-[![GitHub issues](https://img.shields.io/github/issues/NAL-i5K/GFF3toolkit)](https://github.com/NAL-i5K/GFF3toolkit/issues)
-[![GitHub pull requests](https://img.shields.io/github/issues-pr/NAL-i5K/GFF3toolkit)](https://github.com/NAL-i5K/GFF3toolkit/pulls)
 [![Documentation Status](https://readthedocs.org/projects/gff3toolkit/badge/?version=latest)](https://gff3toolkit.readthedocs.io/en/latest/?badge=latest)
 
 ## Background