Add long_description_content_type to setup

Signed-off-by: Jordan Borean <jborean93@gmail.com>

Author: jborean93

setup.py

@@ -289,6 +289,7 @@ def gssapi_modules(lst):
     },
     description='Python GSSAPI Wrapper',
     long_description=long_desc,
+    long_description_content_type='text/x-rst',
     license='LICENSE.txt',
     url="https://github.com/pythongssapi/python-gssapi",
     python_requires=">=3.9",