Fix incorrect configuration option in README

[christophermlne]

forward "/mcp", Hermes.Server.Transport.StreamableHTTP.Plug, server: MyApp.MCPServer

should be:

forward "/mcp", to: Hermes.Server.Transport.StreamableHTTP.Plug, init_opts: [server: MyApp.MCPServer]

[flowerett]

@christophermlne could you explain why it should be done the way you posted?
forward(path, plug, plug_opts \\ [], router_opts \\ []) is the correct macro definition in Phoenix, hex.pm

[zoedsoupe]

phoenix and raw plug macros have this difference

phoenix builds their own on top of plug, that's why we have this difference