Add workflow code coverage report and upload

.github/workflows/codecov.yml

@@ -0,0 +1,25 @@
+name: codecov
+on:
+  push:
+    branches: [main, 0.4.x]
+  pull_request:
+jobs:
+  # Run code coverage using cargo-llvm-cov then upload to codecov.io
+  job_code_coverage:
+    name: llvm-cov
+    runs-on: ubuntu-latest
+    env:
+      CARGO_TERM_COLOR: always
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install Rust
+        run: rustup update stable
+      - name: Install cargo-llvm-cov
+        uses: taiki-e/install-action@cargo-llvm-cov
+      - name: Generate code coverage
+        run: cargo llvm-cov --all-features --workspace --lcov --output-path lcov.info
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v3
+        with:
+          files: lcov.info
+          fail_ci_if_error: true

README.md

@@ -5,6 +5,7 @@
 [![Chrono on crates.io][cratesio-image]][cratesio]
 [![Chrono on docs.rs][docsrs-image]][docsrs]
 [![Join the chat at https://gitter.im/chrono-rs/chrono][gitter-image]][gitter]
+[![codecov.io][codecov-img]][codecov-link]
 
 [gh-image]: https://github.com/chronotope/chrono/actions/workflows/test.yml/badge.svg
 [gh-checks]: https://github.com/chronotope/chrono/actions?query=workflow%3Atest
@@ -14,6 +15,8 @@
 [docsrs]: https://docs.rs/chrono
 [gitter-image]: https://badges.gitter.im/chrono-rs/chrono.svg
 [gitter]: https://gitter.im/chrono-rs/chrono
+[codecov-img]: https://img.shields.io/codecov/c/github/chronotope/chrono?logo=codecov
+[codecov-link]: https://codecov.io/gh/chronotope/chrono
 
 Chrono aims to provide all functionality needed to do correct operations on dates and times in the
 [proleptic Gregorian calendar](https://en.wikipedia.org/wiki/Proleptic_Gregorian_calendar):