Add long description to package information

[palango]

Fixes #567

[codecov]

Codecov Report

Merging #568 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #568   +/-   ##
======================================
  Coverage    90.7%   90.7%           
======================================
  Files          36      36           
  Lines        2346    2346           
  Branches      297     297           
======================================
  Hits         2128    2128           
+ Misses        164     163    -1     
- Partials       54      55    +1

Impacted Files	Coverage Δ
src/raiden_libs/database.py	88.4% <0%> (-2.9%)	⬇️
src/pathfinding_service/api.py	95.81% <0%> (+0.83%)	⬆️

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[karlb]

It looks like this is causing a docker build failure: https://cloud.docker.com/u/raidennetwork/repository/registry-1.docker.io/raidennetwork/raiden-services/builds/f03de662-9c3b-44aa-ae75-c811d3696036

[palango]

Mh, this error message doesn't tell me much. Any ideas?

 ERROR: Command errored out with exit status 1:
command: /usr/local/bin/python3 -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/services/setup.py'"'"'; __file__='"'"'/services/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info

[karlb]

The interesting part is

Complete output (5 lines):
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/services/setup.py", line 31, in <module>
with open("README.md") as readme_file:
FileNotFoundError: [Errno 2] No such file or directory: 'README.md'
----------------------------------------