fix: add marketplace.json so /plugin marketplace add works (#74)

fix: add marketplace.json so the repo can be added with /plugin marketplace add

Claude Code requires `.claude-plugin/marketplace.json` to register a repo
as a plugin marketplace; `plugin.json` alone causes:

    Error: Marketplace file not found at .../.claude-plugin/marketplace.json

This adds a minimal single-plugin marketplace pointing at the repo root,
and updates the README install steps to match what actually works
(`/plugin marketplace add` then `/plugin install`).

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -0,0 +1,15 @@
+{
+  "name": "launchdarkly-ai-tooling",
+  "owner": {
+    "name": "LaunchDarkly",
+    "email": "support@launchdarkly.com",
+    "url": "https://launchdarkly.com"
+  },
+  "plugins": [
+    {
+      "name": "launchdarkly",
+      "description": "LaunchDarkly agent skills and MCP servers for feature flag management, AgentControl, and metrics",
+      "source": "."
+    }
+  ]
+}

README.md

@@ -52,10 +52,13 @@ Agent Skills are modular, text-based playbooks that teach an agent how to perfor
 
 This repo is a [Claude Code plugin](https://code.claude.com/docs/en/create-plugins). Installing it gives you all the skills above plus the LaunchDarkly MCP server.
 
-1. Open Claude Code and run `/plugin install`.
-2. Search for **LaunchDarkly**, or install directly from the repo URL:
+1. Add this repo as a plugin marketplace in Claude Code:
    ```
-   https://github.com/launchdarkly/ai-tooling
+   /plugin marketplace add launchdarkly/ai-tooling
+   ```
+2. Install the plugin:
+   ```
+   /plugin install launchdarkly@launchdarkly-ai-tooling
    ```
 3. Authenticate the LaunchDarkly MCP server when prompted with your [API access token](https://docs.launchdarkly.com/home/account/api).