How to set up diff_drive_controller?

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I want to properly set the odometry for my 2W robot and decided to use diff_drive_controller for that. I got a bit confused by reading the wiki page. It says that the package subscribes to cmd_vel and publishes odometry based on that. Does it mean that I do not need any encoders to send?

Also, a quick question regarding the wheels. The package also asks for the wheel joints and I have descrbied them in my xacro file:

<joint name="wheel_left_joint" type="continuous">
    <parent link="base_link"/>
    <child link="wheel_left_link"/>
    <origin xyz="0.0 0.08 0.023" rpy="-1.57 0 0"/>
    <axis xyz="0 0 1"/>
  </joint>

  <link name="wheel_left_link">
    <visual>
      <origin xyz="0 0 0" rpy="1.57 0 0"/>
      <geometry>
        <mesh filename="package://turtlebot3_description/meshes/wheels/left_tire.stl" scale="0.001 0.001 0.001"/>
      </geometry>
      <material name="dark"/>
    </visual>

And if I use gazebo:

<gazebo reference="wheel_left_link">
    <mu1>0.1</mu1>
    <mu2>0.1</mu2>
    <kp>500000.0</kp>
    <kd>10.0</kd>
    <minDepth>0.001</minDepth>
    <maxVel>0.1</maxVel>
    <fdir1>1 0 0</fdir1>
    <material>Gazebo/FlatBlack</material>
  </gazebo>

The wheels get their TF but how can I enable TF when I use a real robot? For some reason they are missing.