docs: Formatting of SSE server mounting example in README

Author: comfuture

README.md

@@ -360,9 +360,11 @@ from mcp.server.fastmcp import FastMCP
 mcp = FastMCP("My App")
 
 # Mount the SSE server to the existing ASGI server
-app = Starlette(routes=[
-    Mount('/', app=mcp.sse_app())
-])
+app = Starlette(
+    routes=[
+        Mount('/', app=mcp.sse_app()),
+    ]
+)
 
 # or dynamically mount as host
 app.router.routes.append(Host('mcp.acme.corp', app=mcp.sse_app()))