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

docs_src/client_callbacks/tutorial001.py

@@ -0,0 +1,19 @@
+from pydantic import BaseModel
+
+from mcp.server import MCPServer
+from mcp.server.mcpserver import Context
+
+mcp = MCPServer("Library")
+
+
+class CardHolder(BaseModel):
+    name: str
+
+
+@mcp.tool()
+async def issue_card(ctx: Context) -> str:
+    """Issue a new library card."""
+    answer = await ctx.elicit("What name should go on the card?", schema=CardHolder)
+    if answer.action == "accept":
+        return f"Card issued to {answer.data.name}."
+    return "No card issued."