docs: add README with badges and rule documentation

Author: swernerx

README.md

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+# eslint-plugin-lingui-typescript
+
+[![npm version](https://img.shields.io/npm/v/eslint-plugin-lingui-typescript.svg)](https://www.npmjs.com/package/eslint-plugin-lingui-typescript)
+[![CI](https://github.com/user/eslint-plugin-lingui-typescript/actions/workflows/ci.yml/badge.svg)](https://github.com/user/eslint-plugin-lingui-typescript/actions/workflows/ci.yml)
+[![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](https://opensource.org/licenses/MIT)
+
+ESLint plugin for [Lingui](https://lingui.dev/) with TypeScript type-aware rules.
+
+## Features
+
+- 🔍 Detects incorrect usage of Lingui translation macros
+- 📝 Enforces simple, safe expressions inside translated messages
+- 🎯 Detects missing localization of user-visible text
+- 🧠 Respects TypeScript types to avoid false positives (e.g. string literal unions)
+
+## Requirements
+
+- Node.js ≥ 24
+- ESLint ≥ 9
+- TypeScript ≥ 5 (optional, for type-aware rules)
+
+## Installation
+
+```bash
+npm install --save-dev eslint-plugin-lingui-typescript
+```
+
+## Usage
+
+### ESLint Flat Config (eslint.config.ts)
+
+```ts
+import linguiPlugin from "eslint-plugin-lingui-typescript"
+
+export default [
+  // Use recommended config
+  linguiPlugin.configs["flat/recommended"],
+
+  // Or configure rules manually
+  {
+    plugins: {
+      "lingui-ts": linguiPlugin
+    },
+    rules: {
+      "lingui-ts/no-single-variable-message": "error"
+    }
+  }
+]
+```
+
+## Rules
+
+| Rule | Description | Recommended |
+|------|-------------|:-----------:|
+| [no-single-variable-message](docs/rules/no-single-variable-message.md) | Disallow messages that consist only of a single variable | ✅ |
+
+### Planned Rules
+
+- `no-complex-expressions-in-message` — Restrict complexity of expressions in messages
+- `no-nested-macros` — Disallow nesting Lingui macros
+- `no-single-tag-message` — Disallow messages with only a single markup tag
+- `valid-t-call-location` — Enforce valid locations for `t` macro calls
+- `no-unlocalized-strings` — Detect user-visible strings not wrapped in Lingui
+- `text-restrictions` — Enforce project-specific text restrictions
+- `consistent-plural-format` — Ensure consistent plural usage
+
+## License
+
+[MIT](LICENSE)
+

docs/rules/no-single-variable-message.md

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+# no-single-variable-message
+
+Disallow Lingui messages that consist only of a single variable.
+
+## Why?
+
+Messages containing only a variable provide no context for translators and cannot be properly translated. The translator has no way of knowing what the variable represents or how to adapt the translation for different languages.
+
+## Rule Details
+
+This rule reports Lingui messages (`t` tagged templates and `<Trans>` components) that contain only a single variable with no surrounding text.
+
+### ❌ Invalid
+
+```tsx
+// Template literal with only a variable
+t`${status}`
+t`${user.name}`
+t` ${status} `  // whitespace doesn't count as text
+
+// JSX with only a variable
+<Trans>{label}</Trans>
+<Trans>{user.name}</Trans>
+<Trans>  {status}  </Trans>
+```
+
+### ✅ Valid
+
+```tsx
+// Template literal with text
+t`Status: ${status}`
+t`Hello ${name}`
+t`${count} items`
+
+// Multiple variables are fine (implies structure)
+t`${first} and ${second}`
+
+// JSX with text
+<Trans>Hello {name}</Trans>
+<Trans>Status: {status}</Trans>
+<Trans>{count} items remaining</Trans>
+
+// Plain text is fine
+t`Hello World`
+<Trans>Hello World</Trans>
+```
+
+## Options
+
+This rule has no options.
+
+## When Not To Use It
+
+If you have valid use cases for single-variable messages and handle the translation context elsewhere, you can disable this rule.
+