Create a License for the documents

[sehlen-bsi]

No description provided.

[lieser]

For the License we probably need/want to distinguish between the source code for all the helper scripts and the documents.

I'm unsure how well licenses for source code fit to documents.

Source code

Here it probably makes most sense to use the BSD 2-Clause "Simplified" License, the same as Botan is using. Especially since some scripts are modified versions of the ones inside Botan.

Documents

Currently I think all or nearly all documents are claiming to be owned by the BSI. And have rather strict limitations on reuse.
I think it would be great to relax this a lot, and release the documents under a license that better goes along with the open source idea that Botan is following.
But this is probably something that we need to discuss internally first.