docs: add Claude Code usage example to README files (#117)

I verified this is working:

```bash
$ claude mcp list | grep gitea
gitea: go run gitea.com/gitea/gitea-mcp@latest -t stdio - ✓ Connected
```

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/117
Reviewed-by: hiifong <f@f.style>
Co-authored-by: silverwind <me@silverwind.io>
Co-committed-by: silverwind <me@silverwind.io>

README.md

@@ -13,6 +13,7 @@
   - [What is Gitea?](#what-is-gitea)
   - [What is MCP?](#what-is-mcp)
   - [🚧 Installation](#-installation)
+    - [Usage with Claude Code](#usage-with-claude-code)
     - [Usage with VS Code](#usage-with-vs-code)
     - [📥 Download the official binary release](#-download-the-official-binary-release)
     - [🔧 Build from Source](#-build-from-source)
@@ -32,6 +33,17 @@ Model Context Protocol (MCP) is a protocol that allows for the integration of va
 
 ## 🚧 Installation
 
+### Usage with Claude Code
+
+This method uses `go run` and requires [Go](https://go.dev) to be installed.
+
+```bash
+claude mcp add --transport stdio gitea \
+  --env GITEA_ACCESS_TOKEN=token \
+  --env GITEA_HOST=https://gitea.com \
+  -- go run gitea.com/gitea/gitea-mcp@latest -t stdio
+```
+
 ### Usage with VS Code
 
 For quick installation, use one of the one-click install buttons at the top of this README.