docs(readme): Create README.md

README.md

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+# sponsorblockcast-go
+
+A Go program that skips sponsored YouTube content and skippable ads on all local Google Cast devices, using the [SponsorBlock](https://github.com/ajayyy/SponsorBlock) API. This project was inspired by [sponsorblockcast](https://github.com/nichobi/sponsorblockcast), but written from scratch to decrease memory and CPU usage, and to work around some of its problems (see [Differences from sponsorblockcast](#differences-from-sponsorblockcast)).
+
+This program will scan for all Google Cast devices on the LAN, and runs a Goroutine for each one to efficiently poll its status every minute. If a Cast device is found to be playing a YouTube video, the poll interval is increased to once every second, sponsored segments are fetched from the SponsorBlock API and stored in memory. Whenever the Cast device reaches a sponsored segment, the program tells it to seek to the end of the segment.
+
+Additionally, sponsorblockcast-go will look for skippable YouTube ads, and automatically hit the skip button when it becomes available.
+
+## Installation
+
+### Docker Image
+You can [install Docker](https://docs.docker.com/engine/install/) directly or use [Docker Compose](https://docs.docker.com/compose/install/) (Or use Podman, Portainer, etc). Please note you *MUST* use the 'host' network as shown below for CLI Docker or in the example for `docker-compose`.
+
+#### Docker
+Run the below commands as root or a member of the `docker` group:
+```shell
+docker run --network=host --name=sponsorblockcast-go ghcr.io/gabe565/sponsorblockcast-go
+```
+
+#### Docker Compose
+First you will need a `docker-compose.yaml` file, such as the [one included in this repo](docker-compose.yaml). Run the below commands as root or a member of the `docker` group:
+```shell
+docker compose up -d
+```
+
+### Manual Installation
+#### Instructions
+
+Download and run the [latest release binary](https://github.com/gabe565/sponsorblockcast-go/releases/latest) for your system and architecture.
+
+## Usage
+Run `sponsorblockcast-go` from a terminal or activate the service with `systemctl enable --now sponsorblockcast-go`.
+
+## Configuration
+You can configure the following parameters by setting the appropriate command line flag or environment variable:
+
+| Flag                 | Env                                   | Description                                                                                                                                                        | Default  |
+|----------------------|---------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------|
+| `--paused-interval`  | `SBC_PAUSED_INTERVAL`                 | Time to wait between each poll of the Cast device status when paused.                                                                                              | `1m`     |
+| `--playing-interval` | `SBC_PLAYING_INTERVAL`                | Time to wait between each poll of the Cast device status when playing.                                                                                             | `1s`     |
+| `--categories`       | `SBC_CATEGORIES` (or `SBCCATEGORIES`) | Comma-separated (or space-separated) SponsorBlock categories to skip, see [category list](https://github.com/ajayyy/SponsorBlock/blob/master/config.json.example). | `sponsor` |
+| `--interface`         | `SBC_INTERFACE` | Optionally configure the network interface to use.                                                                                                                 |          |
+
+To modify the variables when running as a systemd service, create an override for the service with:
+
+```shell
+sudo systemctl edit sponsorblockcast-go.service
+```
+
+This will open a blank override file where you can specify environment variables like so:
+```
+[Service]
+Environment="SBC_PAUSED_INTERVAL=1m"
+Environment="SBC_PLAYING_INTERVAL=1s"
+Environment="SBC_CATEGORIES=sponsor,selfpromo"
+```
+
+To modify the variables when running as a Docker container, you can add arguments to the `docker run` command like so:
+
+```shell
+docker run --network=host --env SBC_PAUSED_INTERVAL=5m --env SBC_PLAYING_INTERVAL=2s --name=sponsorblockcast-go ghcr.io/gabe565/sponsorblockcast-go
+```
+
+When using `docker-compose.yaml`, you can simply edit the `environment` directive as shown in the example file.
+
+## Differences from sponsorblockcast
+- Compiles to a single binary.
+- Scan interval less often when a YouTube video is not playing, resulting in lower CPU and less stress on the Cast device.
+- Written Go, which is the same language as `go-chromecast`. This means `go-chromecast` functions can be called directly instead of relying on shell scripts, child commands, or string parsing.
+- `go-chromecast` only needs to be loaded once within a single Go program, resulting on lower memory usage.
+
+I own 12 Google Cast devices, and have compared CPU and memory usage of the two programs. Note that CPU usage is measured in "milliCPU", meaning that 1m is equal to 1/1000 of a CPU. Here are the averages:
+
+| Program             | CPU | Memory |
+|---------------------|-----|--------|
+| sponsorblockcast    | 75m | 70Mi   |
+| sponsorblockcast-go | 1m  | 10Mi   |