By default, custom shaders are available in the Unsorted group of the Arnold Shader Network Editor (they are not visible in the Material Browser directly). You can define a group to your shader with the following steps. For example to add myshader to Arnold/Shader/Surface/Mymenu:
Create a .mtd meta data file (in this example it is myshader.mtd) and place it next to your shader.
Add the menu path and the command id to the meta data file. Command id must be a unique id obtained from Plugin Café.
If you have your own C4D node for your shader, you can use its id as the command id.