Add coverage report from coveralls.io

[vaivaswatha]

It will show what code is not covered by tests. Here is a job for this I'm using in a github actions workflow:

  test_coverage:
    name: Code coverage in tests
    runs-on: ubuntu-latest
    container:
      image:                    xd009642/tarpaulin:latest
      options:                  --security-opt seccomp=unconfined
    steps:
      - name:                   Checkout repository
        uses:                   actions/checkout@v2
      - name:                   Generate code coverage
        run: |
          cargo tarpaulin --verbose --all-features --workspace --timeout=360 --out Lcov
      - name: Push code coverage results to coveralls.io
        uses: coverallsapp/github-action@master
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          path-to-lcov: ./lcov.info

Originally posted by @greenhat in #5 (comment)