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

docs_src/context/tutorial002.py

@@ -0,0 +1,17 @@
+from mcp.server import MCPServer
+from mcp.server.mcpserver import Context
+
+mcp = MCPServer("Bookshop")
+
+
+@mcp.resource("catalog://genres")
+def genres() -> str:
+    """The genres the catalog is organised into."""
+    return "fiction, non-fiction, poetry"
+
+
+@mcp.tool()
+async def describe_catalog(ctx: Context) -> str:
+    """Describe how the catalog is organised."""
+    [contents] = await ctx.read_resource("catalog://genres")
+    return f"The catalog is organised into: {contents.content}"