Use Codecov for recording and reporting code coverage information

Author: per1234

Diff for: .github/workflows/test.yml

@@ -49,3 +49,11 @@ jobs:
 
       - name: Run unit tests
         run: task go:test-unit
+
+      - name: Send unit tests coverage to Codecov
+        if: matrix.operating-system == 'ubuntu-latest'
+        uses: codecov/codecov-action@v1
+        with:
+          file: ./coverage_unit.txt
+          flags: unit
+          fail_ci_if_error: true

Diff for: README.md

@@ -1,5 +1,7 @@
 # arduino-check
 
+[![codecov-badge]](https://codecov.io/gh/arduino/arduino-lint)
+
 `arduino-check` is a command line tool that automatically checks for common problems in your
 [Arduino](https://www.arduino.cc/) projects: