fix: warning from twine check

Author: vinitkumar

setup.py

@@ -35,6 +35,7 @@
     install_requires=requirements,
     license="Apache Software License 2.0",
     long_description=readme + "\n\n" + history,
+    long_description_content_type="text/x-rst",
     include_package_data=True,
     keywords="json2xml",
     name="json2xml",