Code Generation : Add primary key / foreign key to Entity Framework

I'm using EF with database first approach.

I would like to add attribute to the generated code to mark property as primary key / foreign key when it's the case.

For example, if I have a table User in my database

CREATE TABLE User
(
   Id int PRIMARY KEY
);

I would like my generated code to include an attribute that indicate that Id is the primary key.

public partial class User
{
    [PrimaryKey]
    public int Id { get; set; }
}

How could I do that?

EDIT : I know about T4 template, I just don't know where to start to modify that file.