Add README, fix Node.js 24 deprecation in release workflow.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -0,0 +1,96 @@
+# sgard — Shimmering Clarity Gardener
+
+A dotfiles manager that checkpoints files into a portable repository and
+restores them on demand.
+
+The repository is a single directory that can live anywhere — local disk,
+USB drive, NFS mount — making it portable between machines.
+
+## Installation
+
+Homebrew:
+
+```
+brew tap kisom/homebrew-tap
+brew install sgard
+```
+
+From source:
+
+```
+git clone https://github.com/kisom/sgard && cd sgard
+go build -o sgard ./cmd/sgard
+```
+
+Or install into `$GOBIN`:
+
+```
+go install github.com/kisom/sgard/cmd/sgard@latest
+```
+
+Binaries are also available on the
+[releases page](https://github.com/kisom/sgard/releases).
+
+## Quick start
+
+```sh
+# Initialize a repo (default: ~/.sgard)
+sgard init
+
+# Track some dotfiles
+sgard add ~/.bashrc ~/.gitconfig ~/.ssh/config
+
+# Checkpoint current state
+sgard checkpoint -m "initial"
+
+# Check what's changed
+sgard status
+
+# Restore from the repo
+sgard restore
+```
+
+Use `--repo` to put the repository somewhere else, like a USB drive:
+
+```sh
+sgard init --repo /mnt/usb/dotfiles
+sgard add ~/.bashrc --repo /mnt/usb/dotfiles
+sgard restore --repo /mnt/usb/dotfiles
+```
+
+## Commands
+
+| Command | Description |
+|---|---|
+| `init` | Create a new repository |
+| `add <path>...` | Track files, directories, or symlinks |
+| `remove <path>...` | Stop tracking files |
+| `checkpoint [-m msg]` | Re-hash tracked files and update the manifest |
+| `restore [path...] [-f]` | Restore files to their original locations |
+| `status` | Show which tracked files have changed |
+| `diff <path>` | Show content diff between stored and current file |
+| `list` | List all tracked files |
+| `verify` | Check blob store integrity against manifest hashes |
+| `version` | Print the version |
+
+## How it works
+
+sgard stores files in a content-addressable blob store keyed by SHA-256.
+A YAML manifest tracks each file's original path, hash, type, permissions,
+and timestamp.
+
+```
+~/.sgard/
+  manifest.yaml        # human-readable manifest
+  blobs/
+    a1/b2/a1b2c3d4...  # file contents stored by hash
+```
+
+On `restore`, sgard compares the manifest timestamp against the file's
+mtime. If the manifest is newer, the file is restored without prompting.
+Otherwise, sgard asks for confirmation (`--force` skips the prompt).
+
+Paths under `$HOME` are stored as `~/...` in the manifest, making it
+portable across machines with different usernames.
+
+See [ARCHITECTURE.md](ARCHITECTURE.md) for full design details.