Add content type for long description for twine

Extend setup.py with the following to silence twine warning:
  long_description_content_type="text/x-rst",

Signed-off-by: Lott, Christopher (cl778h) <cl778h@att.com>
Change-Id: I831e38f56a42d9ff46da9b1b2aa47eee26e4ecd2
diff --git a/src/bindings/rmr-python/setup.py b/src/bindings/rmr-python/setup.py
index c1b3148..1d11d50 100644
--- a/src/bindings/rmr-python/setup.py
+++ b/src/bindings/rmr-python/setup.py
@@ -52,4 +52,5 @@
     data_files=[("", ["LICENSE.txt"])],
     install_requires=[],
     long_description=_long_descr(),
+    long_description_content_type="text/x-rst",
 )