Copyright holders are missing from the License file

[ramiromagno]

We forgot to update the Apache License with the copyright holders (at the end of the file):

sdtm.oak/LICENSE.md

Line 182 in 453926b

Copyright [yyyy] [name of copyright owner]

This is important to do as without this clarification the copyright of the code is very fragmented and the authorship of each function / line of code / file rests with the developer who wrote it.

Reading CRAN Extensions on licensing, we can see that we should avoid something like "Name-of-package authors".

Also, the authors should be indicated in decreasing order of contribution. Given the current state of contributions to the package I'd like to suggest:

• F. Hoffmann-La Roche AG
• Pattern Institute
• Atorus Research LLC
• Transition Technologies Science sp. z o.o.