upload to pypi fails due to Readme rendering issues
# Description

Upload with twine to pypi of 4.2.4 fails:
```
twine check dist/pywps-4.2.4.tar.gz 
Checking dist/pywps-4.2.4.tar.gz: FAILED
  `long_description` has syntax errors in markup and would not be rendered on PyPI.
    line 54: Warning: Inline literal start-string without end-string.
  warning: `long_description_content_type` missing.  defaulting to `text/x-rst`.
```

Maybe we should add this check to travis CI.

# Environment

- operating system:
- Python version:
- PyWPS version: 4.2.4
- source/distribution
 - [ ] git clone
 - [ ] Debian
 - [ ] PyPI
 - [ ] zip/tar.gz
 - [ ] other (please specify): 
- web server
 - [ ] Apache/mod_wsgi
 - [ ] CGI
 - [ ] other (please specify): 

# Steps to Reproduce

# Additional Information


diff --git a/setup.py b/setup.py
index 66a2432..ab87755 100644
--- a/setup.py
+++ b/setup.py
@@ -32,6 +32,7 @@ CONFIG = {
     'version': VERSION,
     'description': DESCRIPTION,
     'long_description': LONG_DESCRIPTION,
+    'long_description_content_type': 'text/markdown',
     'keywords': KEYWORDS,
     'license': 'MIT',
     'platforms': 'all',
['setup.py']