Add README.md and make the template workflow explicit in CLAUDE.md

README covers the copy-clone-rename-build flow and the simple cargo/nix
run commands. CLAUDE.md now states the intended workflow up front
(rename script, then build whatever the user actually wants) instead
of only implying it via the rename-script section.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018ALEXkc7pTro7tF1WcUuKb

README.md

@@ -0,0 +1,37 @@
+# rust_template
+
+A minimal Rust project template: a `clap` CLI backed by a library crate, with unit tests, an
+integration test, a `criterion` benchmark, and a Nix flake (crane + fenix) — so it builds the same
+way with plain `cargo` or with `nix`.
+
+## Using this template
+
+1. Copy/clone this repo.
+2. Rename the placeholder crate name:
+   ```bash
+   ./scripts/rename-project.sh my_project
+   cd .. && mv rust_template my_project && cd my_project
+   ```
+3. Build whatever you actually came here for — replace `greet` in `src/lib.rs`, extend the CLI in
+   `src/main.rs`, add your own tests and benchmarks.
+
+## Building and running
+
+**With Cargo** (needs Rust installed, or run inside `nix develop`):
+```bash
+cargo run -- Zeke        # build + run, prints "Hello, Zeke!"
+cargo build --release
+cargo test                 # unit + integration tests
+cargo bench                 # criterion benchmark
+```
+
+**With Nix** (no local Rust install needed):
+```bash
+nix develop              # dev shell with the pinned toolchain + tools
+nix build                 # produces ./result/bin/rust_template
+nix run -- Zeke             # build + run
+nix flake check              # clippy, fmt, doc, audit, tests — all in one go
+nix fmt                       # format Rust, Nix, and TOML files
+```
+
+See `CLAUDE.md` for more detail on the project layout and how the pieces fit together.