diff --git a/README.md b/README.md
index 7a9a963..fed618c 100644
--- a/README.md
+++ b/README.md
@@ -52,7 +52,7 @@ In this workshop you will:
 * Add your workspace overlay to the shell startup script for sourcing everytime you open a new console:
   * Add [this](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/bashrc_overlay.bash) to the end of .bashrc (`sudo nano .bashrc`)
   * In [this template](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/bashrc_overlay.bash) find all instances of "`~/ws_overlay_foxy`" and replace it with the path to your own _colcon_ workspace (replace `~/` with `$HOME` for representing the home directory variable in bash scripts)
-* Create custom message (*.msg) or service (*.srv) files in order to create custom interfaces to exchange information between nodes. For this you can use the pre-made `/custom_interface` package and add your own *.msg and/or *.srv files using this [instruction document](None) (__easy__), or you can start from scratch by following [these instructions](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/instructions_custom_topics.md) (__hard__).
+* Create custom message (*.msg) or service (*.srv) files in order to create custom interfaces to exchange information between nodes. For this you can use the pre-made `/custom_interface` package and add your own *.msg and/or *.srv files using this [instruction document](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/srv_tests/src/custom_interfaces/Readme.md) (__easy__), or you can start from scratch by following [these instructions](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/instructions_custom_topics.md) (__hard__).
 
 ## Rules and Standard
 In order for your code to work and to prevent major problems please read through [this document](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/Programming_Rules.md). This will give you a brief oversight over how to develop a ROS2 package using Python.