Rebuild the docs around tested examples; shrink README.v2.md to a pitch (#2978)

docs_src/index/tutorial001.py

@@ -0,0 +1,15 @@
+from mcp.server import MCPServer
+
+mcp = MCPServer("Demo")
+
+
+@mcp.tool()
+def add(a: int, b: int) -> int:
+    """Add two numbers."""
+    return a + b
+
+
+@mcp.resource("greeting://{name}")
+def greeting(name: str) -> str:
+    """Greet someone by name."""
+    return f"Hello, {name}!"