RST formatting in README fixed

Author: Bastian Bechtold

README.rst

@@ -170,6 +170,7 @@ https://freedesktop.org/software/pulseaudio/doxygen/channelmap_8h.html
 Since the mapping of position indices to audio channels is not obvious, a
 dictionary containing all possible positions and channel indices can be
 retrieved by calling ``channel_name_map()``. The positions for the indices up to 10 are: ::
+
     'mono': -1,
     'left': 0,
     'right': 1,

setup.py

@@ -23,6 +23,7 @@
         'Topic :: Multimedia :: Sound/Audio :: Players',
     ],
     long_description=open('README.rst').read(),
+    long_description_content_type='text/x-rst',
     entry_points={
         "pyinstaller40": [
             "hook-dirs = soundcard.__pyinstaller:get_hook_dirs",