Add rust-cache composite action

README.md

@@ -1,3 +1,39 @@
 # actions-rust
 
-Reusable Rust setup + cache action for Gitea Actions
+Reusable Gitea Actions for Rust projects.
+
+## actions/rust-cache
+
+Composite action that installs a Rust toolchain and caches cargo/crate dependencies.
+
+### Usage
+
+```yaml
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: https://gitea.com/actions/checkout@v4
+
+      - name: Setup Rust + Cache
+        uses: https://git.ericxliu.me/eric/actions-rust/.gitea/actions/rust-cache@main
+        with:
+          toolchain: stable  # optional, defaults to stable
+
+      - run: cargo build --release
+      - run: cargo test
+```
+
+### What it does
+
+1. **Cache restore** — Restores `~/.cargo/registry`, `~/.cargo/git`, `~/.rustup/toolchains`, and `target/` using Gitea's native `actions/cache`.
+2. **Rust install** — Runs `rustup` to install or verify the requested toolchain.
+3. **PATH setup** — Appends `$HOME/.cargo/bin` to `$GITHUB_PATH` so cargo/rustc are available in subsequent steps.
+
+### Cache key format
+
+```
+rust-linux-{hash(Cargo.lock)}{hash(Cargo.toml)}
+```
+
+Warm builds run in ~40–60s vs ~3min for a cold build.