After adding repository to overlay, package still not in package path

edit

I'm currently getting into ROS and rosbuild and as start I'm working trough this tutorial, but I'm stuck at:

Adding repositories to the overlay

I did the following things before that point:

rosws init . /opt/ros/kinetic
source setup.zsh
mkdir sandbox
myros rosws set sandbox

Now the basic Overlay is set up, i can access the package roscpp with roscd roscpp and after that I am able to return to my new overlay with roscd - so i add a repository

rosws set turtlebot --git -u https://github.com/turtlebot/turtlebot
rosws update

My .rosinstall file looks like this at this moment:

setup-file: {local-name: /opt/ros/kinetic/setup.sh}
other: {local-name: sandbox}
git: {local-name: turtlebot, uri: 'https://github.com/turtlebot/turtlebot'}

After that the Tutorial says:

After re-sourcing setup.bash the new overlayed stack turtlebot should be in your package path, i.e. roscd turtlebot should switch to the directory ~/fuerte_workspace/turtlebot.

If i want to use roscd turtlebot I'm getting:

roscd: No such package 'turtlebot'

Because the tutorial says

After re-sourcing setup.bash should be in your package path...

I tried resourcing with source source.zsh but thats now working either. What am i doing wrong?