README.md: write initial usage instructions

README.md

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+# PulseAudio auto-ducker
+
+A simple script that ducks the volume of music applications when it detects audio playback.
+
+## Description
+
+The auto-ducker is a simple script to duck the volume of music applications during playback.
+To detect music applications, the script looks for applications running on the PulseAudio sound server with the media role set to _music_.
+The script considers any other application running on the PulseAudio sound server as playback and ducks the volume of music applications.
+
+The auto-ducker has been tested and works with Spotify and [Amberol](https://gitlab.gnome.org/World/amberol).
+The script runs asynchronously every second to minimize resource use.
+
+## Getting Started
+
+### Dependencies
+
+The script uses [mhthies/pulsectl-asyncio](mhthies/pulsectl-asyncio), and so it only works on systems that use the PulseAudio sound server.
+
+* PulseAudio sound server
+
+### Installing
+
+- Clone the repository and create a virtual environment: `python -m venv venv`
+- Activate the virtual environment (`source venv/bin/activate`) and install the requirements: `pip install -r requirements.txt`
+
+### Executing program
+
+The script can be run in two ways: manually, as a script, or automatically on start-up, as a server.
+You can run the script manually when needed by following the next steps:
+
+- Navigate to the script location and activate the virtual environment (`source venv/bin/activate`)
+- Run the script using `./main.py`
+- When ready, close the script using `CTRL+C`
+
+Alternatively, you can run the script as a service on boot.
+Running the script as a service requires a slightly more complex setup:
+
+- Create a service in `/etc/systemd/system/auto-ducker.service` by copying the template from `auto-ducker.service`
+- Fill in the following variables in the template:
+	- `USERID`: your user ID; you can find it using `printenv | grep XDG_RUNTIME_DIR`
+	- `USER`: your username; you can find it using `echo ${USER}`
+	- `GROUP`: your user's group, normally the same as your user name
+	- `/PATH/TO`: the path to this repository
+- Test the service using `sudo systemctl start autho-ducker.service`
+- Enable the service to start on boot using `sudo systemctl enable auto-ducker.service`.
+
+## Help
+
+### Configuration
+
+The script configuration is at the beginning of the `main.py` script.
+You can configure the following variables:
+
+- `DURATION`: how long to spend ducking volume (in milliseconds; default: 2 seconds; minimum: 0)
+- `DUCK`: the minimum volume to which to duck the volume ofmusic applications (default: 0.4; minimum: 0; maximum: 1)
+- `STEPS`: how smooth the auto-ducking (default: 30); larger values lower performance but make ducking and unducking smoother (minimum: 1)
+- `FADE`: the fade function used to duck and unduck the volume of music applications (default: `bezier`); see the end of the script for fade functions
+
+### Debug
+
+You can debug the main script by running it manually, as described above, and observing errors in the output.
+
+When running the auto-ducker as a service, the errors are written to the journal.
+You can view the journal entries for the auto-ducker service using: `sudo journalctl -u auto-ducker.service -f`.
+
+Remember that whenever you edit the service configuration, you need to reload the service configuration (`sudo systemctl daemon-reload`) and restart the service (`sudo systemctl restart auto-ducker.service`).
+
+### FAQ
+
+- Why doesn't YouTube duck or unduck?
+  The auto-ducker only ducks the volume of music applications, not browser tabs.
+If you are listening to YouTube on Google Chrome or Firefox, the auto-ducker will see a browser with audio playback, not a music player.
+The auto-ducker has been tested and works with Spotify and [Amberol](https://gitlab.gnome.org/World/amberol).
+
+- Why is there a delay until music applications are unducked?
+  The auto-ducker only detects that playback has stopped when the application releases the PulseAudio sound server.
+Google Chrome, for example, signals that playback has stopped when no tab has played audio for 15 seconds.
+
+## Authors
+
+- [Nicholas Mamo](https://github.com/NicholasMamo/)
+
+## Version History
+
+- 0.1
+	- Initial release
+
+## License
+
+This project is licensed under the MIT License.
+See the LICENSE.md file for details.
+
+## Acknowledgments
+
+* [README.md template](https://gist.github.com/DomPizzie/7a5ff55ffa9081f2de27c315f5018afc) from [DomPizzie](https://gist.github.com/DomPizzie)
+* [mhthies/pulsectl-asyncio](mhthies/pulsectl-asyncio) for the asynchronous PulseAudio API