I have a small "dock" called "plank".
On bottom of the screenshot.
You can deaktivate in "plank --config" that it works as a taskbar.
It will show only programs you drag on it.
I also have a folder "Program Manager", where I store different kinds of "launchers". *.desktop files, symlinks, shell-scripts.sh
When I drag those on plank, they have no individual icon. Shellscripts are shown as textfiles.
Solution:
this tool.
Run the "generate-launchers.sh", it reads the folder ~/desktop/Program Manager
(of course you can edit the short script for a different directory).
The script will create *.desktop files for all it finds there, in:
/home/mark/.local/share/applications/pm-managed/
Now drag some of them on your plank to add them.
To change the icon, run the included 
./icon-picker
It alows you to set a picture using a fileselection dialog with preview.
After the choice, it restarts plank.
Download and technical readme:
https://schinkenpizza.de/linuxfiles/plank-icon-manager/