ci: Report coverage to Coveralls

Author: jpmckinney

.github/workflows/ci.yml

@@ -17,3 +17,6 @@ jobs:
           cache-dependency-path: setup.py
       - run: pip install .[test]
       - run: pytest --cov agatesql
+      - env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: coveralls --service=github

README.rst

@@ -2,6 +2,10 @@
     :target: https://github.com/wireservice/agate-sql/actions
     :alt: Build status
 
+.. image:: https://coveralls.io/repos/wireservice/agate-sql/badge.svg?branch=master
+    :target: https://coveralls.io/r/wireservice/agate-sql
+    :alt: Coverage status
+
 .. image:: https://img.shields.io/pypi/dm/agate-sql.svg
     :target: https://pypi.python.org/pypi/agate-sql
     :alt: PyPI downloads