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

docs_src/prompts/tutorial003.py

@@ -0,0 +1,16 @@
+from typing import Annotated
+
+from pydantic import Field
+
+from mcp.server import MCPServer
+
+mcp = MCPServer("Code Helper")
+
+
+@mcp.prompt(title="Code review")
+def review_code(
+    code: Annotated[str, Field(description="The code to review.")],
+    language: Annotated[str, Field(description="The language the code is written in.")] = "python",
+) -> str:
+    """Review a piece of code."""
+    return f"Please review this {language} code:\n\n{code}"