README: Add PyPI and license badges

Added badges for version and license to README

Signed-off-by: Arthit Suriyawongkul <arthit@gmail.com>

Author: bact

README.md

@@ -1,4 +1,7 @@
-# spdx-python-model
+# SPDX Python model
+
+[![PyPI - Version](https://img.shields.io/pypi/v/spdx-python-model)](https://pypi.org/project/spdx-python-model/)
+![Apache-2.0 license](https://img.shields.io/github/license/spdx/spdx-python-model)
 
 Generated Python code for [SPDX specification version 3][spdx-spec].