Update README.md

Author: ProfLander

README.md

@@ -3,3 +3,18 @@
 `rust-gpu` helper program for automating shader crate compilation.
 
 Can compile once, or run in daemon mode and recompile in response to filesystem changes.
+
+## Usage
+
+`rust-gpu-builder` relies on the `spirv-builder` crate, which in turn relies on the cargo ecosystem
+to configure the appropriate nightly toolchain for `rust-gpu`. As such, it needs to be run from inside a workspace via `cargo run`.
+
+Thus, it's recommended to add `rust-gpu-builder` as a a git submodule of your cargo workspace, and set it up as the default binary target.
+
+### One-shot compilation
+
+`cargo run --release -- <path-to-shader-crate>` will compile the provided shader crate and output `<crate-name>.spv` and `<crate-name>.spv.json` to `target/spirv-unknown-spv1.5/release/deps/`.
+
+### Hot-recompile
+
+`cargo run --release -- <path-to-shader-crate> -w <path-to-watch>` will compile as per the above, then watch the provided path and recompile whenever it changes.