Add github action for coverage (#3)

.github/workflows/coverage.yml

@@ -0,0 +1,30 @@
+name: coverage
+on:
+  pull_request:
+  push:
+    branches:
+      - "main"
+
+jobs:
+  coverage:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/setup-go@v3
+      with:
+        go-version: "1.20"
+    - uses: actions/checkout@v3
+    - run: go test -coverprofile=profile.cov ./...
+    - name: Send coverage
+      uses: shogo82148/actions-goveralls@v1
+      with:
+        path-to-profile: profile.cov
+        parallel: true
+
+  # notifies that all test jobs are finished.
+  finish:
+    needs: coverage
+    runs-on: ubuntu-latest
+    steps:
+    - uses: shogo82148/actions-goveralls@v1
+      with:
+        parallel-finished: true