Add README for @shopify/mcp package

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

Author: tizmagik

packages/mcp/README.md

@@ -0,0 +1,50 @@
+# @shopify/mcp
+
+MCP server for the Shopify Admin API. Connects AI coding agents (Claude, Cursor, etc.) to your Shopify store via the [Model Context Protocol](https://modelcontextprotocol.io).
+
+## Setup
+
+```bash
+claude mcp add shopify -- npx -y -p @shopify/mcp
+```
+
+Optionally set a default store so you don't have to pass it with every request:
+
+```bash
+export SHOPIFY_FLAG_STORE=my-store.myshopify.com
+```
+
+## Tools
+
+### `shopify_auth_login`
+
+Authenticate with a Shopify store. Returns a URL the user must visit to complete login via device auth. After approval, subsequent `shopify_graphql` calls will use the session automatically.
+
+| Parameter | Type | Required | Description |
+|-----------|------|----------|-------------|
+| `store` | string | No | Store domain. Defaults to `SHOPIFY_FLAG_STORE` env var. |
+
+### `shopify_graphql`
+
+Execute a GraphQL query or mutation against the Shopify Admin API. Uses the latest supported API version.
+
+| Parameter | Type | Required | Description |
+|-----------|------|----------|-------------|
+| `query` | string | Yes | GraphQL query or mutation string |
+| `variables` | object | No | GraphQL variables |
+| `store` | string | No | Store domain override. Defaults to `SHOPIFY_FLAG_STORE` env var. |
+| `allowMutations` | boolean | No | Must be `true` to execute mutations. Safety measure to prevent unintended changes. |
+
+## Example
+
+```
+Agent: "List my products"
+
+→ shopify_auth_login(store: "my-store.myshopify.com")
+← "Open this URL to authenticate: https://accounts.shopify.com/activate?user_code=ABCD-EFGH"
+
+[user approves in browser]
+
+→ shopify_graphql(query: "{ products(first: 5) { edges { node { title } } } }")
+← { "products": { "edges": [{ "node": { "title": "T-Shirt" } }, ...] } }
+```