Tutorial about addons making are here, they're sorted in three groups :
photofiltre introduction Windows only, sorry :(
3D : Blender (Simutrans forum)
If you are interested in writing a tutorial, talk about it on the Simutrans'forum.
In case of problems, mistakes in these tutorials, tell it on the Simutrans'forum.
Thanks to the German wiki's autors about .dat files, it was really useful for me.
Thanks to the community who was patient enough to answer my questions (which were often willy …)
Thanks to Fefe for Linux's parts of the tutorial.