add implementation notes

[mtbc]

see https://github.com/mtbc/omero-downloader/blob/overview/IMPLEMENTATION.md

[pwalczysko]

The code's focus on top-level OME Model units is too pervasive. For example, one may need to export annotations that are on channels.

and

The input and output of metadata has incomplete coverage. For example, try importing or exporting OME-XML datasets using OMERO code.

I think it is quite important to capture annotations which are directly on Projects, Datasets and Screen/Plates/Wells. Is it captured by this strategy ? Maybe this point could be more explicit

[mtbc]

Yes, annotations on datasets can be exported with the current code.

[mtbc]

Moving this markdown file to be a Javadoc overview page would make links much easier for even offline use: created https://trello.com/c/N7Y3Dajl/62-overview-page-for-implementation accordingly.