#7 create submodule function

I think it would be better to have a function to create submodules, instead of copy-pasting code for each submodule.

It will also allow the possibility to add submodules after the parent repository creation (for example if one would want a new raw data folder for a new type of data, months after the repo was created).

I started to work on this in add_submodules.sh

It is not yet working, see https://gin.g-node.org/gin4RRI/testproject/src/master/.gitmodules : the submodules seem to be there, but it does not appear...

I think datalad -C ${projectdir} publish --recursive is not publishing all that is needed?

If I do this it then works: cd ${projectdir} gin sync