docs: document Antigravity CLI remote plugin install

Replace the manual clone-and-copy steps for the Antigravity CLI with the
direct `agy plugins install` command from a remote GitHub repository.

Reference: GoogleCloudPlatform/data-agent-kit#46

Author: twishabansal

README.md

@@ -129,29 +129,17 @@ _(Tip: Antigravity 2.0 automatically discovers skills in these directories at th
 
 #### Antigravity CLI
 
-**1. Clone the Repo:**
-
-```bash
-git clone --branch 0.2.0 https://github.com/gemini-cli-extensions/cloud-sql-mysql.git
-```
-
-**2. Install the skills:**
+You can install plugins directly from a remote GitHub repository.
 
-Choose a location for the skills:
-- **Global (all workspaces):** `~/.gemini/antigravity-cli/skills/`
-- **Workspace-specific:** `<workspace-root>/.agents/skills/`
-
-Copy the skill folders from the cloned repository's `skills/` directory to your chosen location:
+**1. Install the plugin:**
 
 ```bash
-cp -R cloud-sql-mysql/skills/* ~/.gemini/antigravity-cli/skills/
+agy plugins install https://github.com/gemini-cli-extensions/cloud-sql-mysql
 ```
 
-**3. Set env vars:**
+**2. Set env vars:**
 Set your environment vars as described in the [configuration section](#configuration).
 
-_(Tip: Antigravity CLI automatically discovers skills in these directories at the start of a session. You can verify they are active by running the `/skills` command in your active session.)_
-
 </details>
 
 <details>