add license to documentation

[tomkralidis]

In the context of OSGeo incubation, suggest to add a license for documentation (see pygeoapi for an example https://github.com/geopython/pygeoapi/blob/master/docs/source/conf.py#L98-L101)

[tomkralidis]

Thanks. Can you point me to the documentation license?

[gfenoy]

The documentation license is here: https://zoo-project.github.io/docs/contribute/howto.html#licensing and also on the documentation home page: https://zoo-project.github.io/docs/index.html

[tomkralidis]

Thanks. Can we make this available more prominently on the documentation (via Sphinx conf) itself? Example: https://github.com/geopython/pygeoapi/blob/master/docs/source/conf.py#L98-L101

[gfenoy]

Done in 0a265d1.