Update readme.

README.md

@@ -1,13 +1,8 @@
-# Setup Rust
+# Setup Rust and Cargo
 
-A GitHub action for setting up Rust and Cargo. Will automatically install the appropriate toolchain
+A GitHub action for setting up Rust and Cargo.
-with `rustup` by inspecting the `RUSTUP_TOOLCHAIN` environment variable or the `rust-toolchain.toml`
-configuration file.
-
-## Installation
 
 ```yaml
-# ...
 jobs:
   ci:
     name: CI
@@ -17,3 +12,97 @@ jobs:
       - uses: moonrepo/setup-rust@v0
       - run: cargo test
 ```
+
+## To Do
+
+- [x] Install Rust toolchain with `rustup`
+- [x] Install Cargo bins with `cargo-binstall`
+- [ ] Cache `~/.cargo` directory (not everything)
+- [ ] Cache `target` directory?
+
+## Configuring the Rust toolchain
+
+This action will automatically install the appropriate toolchain with `rustup` by inspecting the
+`RUSTUP_TOOLCHAIN` environment variable or the `rust-toolchain.toml` (preferred) or `rust-toolchain`
+configuration files. If no toolchain found, will default to `stable`.
+
+```toml
+# rust-toolchain.toml
+[toolchain]
+channel = "1.68.0"
+```
+
+> When loading a configuration file, only the `channel` field is used, while the other fields are
+> ignored. We chose this approach, as those other fields are typically for develop/release
+> workflows, but not for CI, which requires a minimal/granular setup.
+
+The toolchain/channel can also be explicitly configured with the `toolchain` input, which takes
+highest precedence.
+
+```yaml
+- uses: moonrepo/setup-rust@v0
+  with:
+    toolchain: '1.65.0'
+```
+
+### Profile and components
+
+Furthermore, this action supports rustup profiles and components, which can be configured with the
+`profile` and `components` inputs respectively. When not defined, profile defaults to `minimal`.
+
+```yaml
+- uses: moonrepo/setup-rust@v0
+  with:
+    profile: complete
+```
+
+When using components, the input requires a comma separated list of component names.
+
+```yaml
+- uses: moonrepo/setup-rust@v0
+  with:
+    components: clippy
+- run: cargo clippy --workspace
+```
+
+## Installing Cargo binaries
+
+If you require `cargo-make`, `cargo-nextest`, or other global binaries, this action supports
+installing Cargo binaries through the `bins` input, which requires a comma-separated list of crate
+names (`cargo-` prefix optional).
+
+```yaml
+- uses: moonrepo/setup-rust@v0
+  with:
+    bins: nextest, cargo-insta@1.28.0
+```
+
+> Binaries are installed with [`cargo-binstall`](https://crates.io/crates/cargo-binstall) under the
+> hood.
+
+## Compared to
+
+### `actions-rs/*`
+
+The "official" actions have served their purpose, but after 3 years of no updates, server lack of
+maintenance, and being full of deprecation warnings, it was time to create something new.
+
+Outside of being evergreen, this action also supports the following features:
+
+- Installs Cargo bins.
+- Assumes `rustup`, `cargo`, and other commands are available globally. This allows you to use them
+  directly in a `run` command, without having to use `actions-rs/cargo`.
+
+However, this action _does not_:
+
+- Install `rustup` if it does not exist, while `actions-rs` will. This is typically fine if using
+  GitHub provided runners as all Rust tooling comes pre-installed.
+
+### `dtolnay/rust-toolchain`
+
+This action is very similar to `dtolnay/rust-toolchain`, which was a great implementation reference,
+but this action also supports the following features:
+
+- Extracts the toolchain/channel from `rust-toolchain.toml` and `rust-toolchain` configuration
+  files.
+- Installs Cargo bins.