fix README rendering error

Fix for "HTTPError: 400 Client Error: The description failed to render in the default format of reStructuredText"

Author: Arman Zholmyrzayev

setup.py

@@ -25,6 +25,7 @@ def read_file(fname):
     version=version,
     description='Agent for Reporting results of tests to the Report Portal',
     long_description=read_file('README.rst'),
+    long_description_content_type='text/markdown',
     author='Pavel Papou',
     author_email='[email protected]',
     url='https://github.com/reportportal/agent-python-pytest',