add badges in Readme file.

README.md

 # A||GO API-Client python library
 We provide here a simple API client for [A||GO](https://allgo18.inria.fr) written in Python.
 
+[![pipeline status](https://gitlab.inria.fr/allgo/api-clients/python_client/badges/client_api/pipeline.svg)](https://gitlab.inria.fr/allgo/api-clients/python_client/commits/client_api)
+python 2.7: [![coverage report 2.7](https://gitlab.inria.fr/allgo/api-clients/python_client/badges/client_api/coverage.svg?job=tests:2.7)](https://gitlab.inria.fr/allgo/api-clients/python_client/commits/client_api?job=tests:2.7)
+python 3.7: [![coverage report 3.7](https://gitlab.inria.fr/allgo/api-clients/python_client/badges/client_api/coverage.svg?job=tests:3.7)](https://gitlab.inria.fr/allgo/api-clients/python_client/commits/client_api?job=tests:3.7)
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 ## Description
 AllGo is a SaaS (Software as a Service) platform provided by Inria. It may be seen as a virtual showroom of technologies developed by research teams.
 First follow https://allgo18.inria.fr/accounts/signup to create an account on AllGo (anyone may create such an account). Once your account creation is confirmed, please connect to https://allgo18.inria.fr to obtain your private token, which will allow yo to use the AllGo REST API. You will need this token later (cf. §3 below).