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

docs_src/context/tutorial001.py

@@ -0,0 +1,10 @@
+from mcp.server import MCPServer
+from mcp.server.mcpserver import Context
+
+mcp = MCPServer("Bookshop")
+
+
+@mcp.tool()
+def search_books(query: str, ctx: Context) -> str:
+    """Search the catalog by title or author."""
+    return f"[request {ctx.request_id}] Found 3 books matching {query!r}."