Add Contributing guide and Integration Test guidelines

- Link to CONTRIBUTING.md in project root
- New Integration Tests section:
  - Avoid sound output in tests
  - Tips for testing audio sources
  - Suggest examples for audible features
  - Note challenges in automated audio testing

CONTRIBUTING.md

@@ -51,6 +51,21 @@ src/:
   - Rust's robust type system reduces the need for extensive unit testing compared to dynamically typed languages
 - Run tests: `cargo test`
 
+### Integration Tests
+
+When possible, add integration tests for your new features. Keep in mind:
+
+- Typically, these tests should not produce actual sound output (i.e., avoid using `Sink` or `Stream`).
+- For new audio sources:
+  - Verify that samples have changed from their initial state.
+  - Check if samples are non-zero where appropriate.
+  - Look for expected patterns or characteristics in the audio data.
+- Be aware that many aspects of audio processing are challenging to verify automatically.
+- For features requiring audible verification:
+  - Create an example in the `examples/` directory that demonstrates the functionality.
+  - These examples can produce sound for manual testing.
+  - Document the expected behavior in the example's comments.
+
 ## Documentation
 
 - Add inline documentation to all public items

README.md

@@ -24,6 +24,10 @@ See [the docs](https://docs.rs/rodio/latest/rodio/#alternative-decoder-backends)
 
 Rodio uses `cpal` to send audio to the OS for playback. On Linux `cpal` needs the ALSA development files. These are provided as part of the libasound2-dev package on Debian and Ubuntu distributions and alsa-lib-devel on Fedora.
 
+# Contributing
+
+For information on how to contribute to this project, please see our [Contributing Guide](https://github.com/RustAudio/rodio/CONTRIBUTING.md).
+
 ## License
 [License]: #license