setup.py: add long_description_content_type

setup.py

@@ -71,6 +71,18 @@
     'with an emphasis on speech processing.',
     long_description=long_description,
 
+    # Denotes that our long_description is in Markdown; valid values are
+    # text/plain, text/x-rst, and text/markdown
+    #
+    # Optional if long_description is written in reStructuredText (rst) but
+    # required for plain-text or Markdown; if unspecified, "applications should
+    # attempt to render [the long_description] as text/x-rst; charset=UTF-8 and
+    # fall back to text/plain if it is not valid rst" (see link below)
+    #
+    # This field corresponds to the "Description-Content-Type" metadata field:
+    # https://packaging.python.org/specifications/core-metadata/#description-content-type-optional
+    long_description_content_type='text/markdown',  # Optional (see note above)
+
     # The project's main homepage.
     url='https://github.com/fgnt/padertorch/',