Remove docs and paper data/code from release

[matjobst]

This is a fix for #98
There is no way to remove stuff from the source distribution using a config inside pyproject.toml as long as we are using setuptools_scm (see pypa/setuptools_scm#190). As soon as setuptools_scm is used, all data which is under version control is added. The solution proposed by the authors of setuptools_scm is to add a MANIFEST.in.
In the MANIFEST.in, I remove the docs and the paper folders as these should not be required for a source distribution via pypi.
Additrionally I added find={include = ["nir*"]} in the pyproject.toml which will cause only the nir folder to be added to the wheel (the other files should not be required).
I tested it locally and it seems to work. But please also check it, @Jegp .
Resulting sizes are ~19 kB for the wheel and 25 kB for the source.

[Jegp]

Excellent work @matjobst! Great catch. I suggest we just merge it as-is and release. Would you be ok seeing that through? After the changes here, it should be as simple as just pushing a release with a new tag.

[matjobst]

Its released as version 1.0.4 now. Looks good on pypi. A trial install also worked without any immediate issues.