Add a README to the project

It's about time I had a proper README for this thing.

README.md

@@ -0,0 +1,52 @@
+# Another Boids in Rust
+
+This is my implementation of the Boids flocking algorithm. It is written in Rust and built on the Bevy game engine.
+
+## Building & Running
+
+### Desktop/native
+
+You'll need a working Rust toolchain, of course. See the [rustup](https://rustup.rs/) site for the basics.
+
+```sh
+# Install system dependencies
+
+:~$ sudo apt install libasound2-dev libudev-dev pkg-config # Debian 13
+:~$ sudo yum install alsa-lib-devel libgudev-devel ppkgconf-pkg-config # Fedora 42
+
+# Build and run
+:~$ cargo build --release
+:~$ cargo run --release # Or skip the build and only run. Cargo will (re)build as-needed.
+```
+
+### Web
+
+This project creates a "static site," meaning a complete deployment of the site is simply copying the output folder onto a webserver.
+
+1. Build `make -f ./makefile_web web`
+2. Serve `python3 -m http.server -d ./out`
+3. Visit site in browser: `http://localhost:8000`
+
+You can use any HTTP server you like. Here, I'm using the Python3 built-in [http.server module](https://docs.python.org/3/library/http.server.html); which is **NOT** recommended for production use. Don't put that on the Internet! Alternatives include [Miniserve](https://crates.io/crates/miniserve) and [BusyBox](https://busybox.net/). The latter of which I'm using in the Docker image.
+
+### Web, but as a Docker Container
+
+You'll need a working Docker installation. See the [get-docker](https://docs.docker.com/get-started/get-docker/) page for details. The rest of the build and execution is self-contained in the container(s) and will not require additional host tools.
+
+```sh
+:~$ docker build -t boids-website .
+:~$ docker run -it --rm boids-website
+```
+
+You might have to open another terminal to `docker kill <the boids container>`. It doesn't seem to respond to `ctrl+c` and I don't plan to figure out why any time soon.
+
+You may also notice that the Dockerfile doesn't call on the Makefile. This is because the Dockerfile predates the Makefile and I haven't updated it to follow the manual process described above. The result is the same, only now it's in a container and using the BusyBox webserver.
+
+## Controls
+
+| Input | Effect |
+| Mouse | The scanner circle is attached to the mouse cursor. Move it to scan boids within the radius. |
+| Left mouse button | Put scanner into center-of-mass mode |
+| Right mouse button | Put scanner into average velocity mode |
+
+**BUG:** On web builds, the right-click action will *both* switch the scanner mode and open the browser's context menu. You can work around this by closing the menu without left-clicking on the canvas -- click outside the canvas, or use the escape key, etc.