Missing license

[MakisH]

While the content is licensed under CC BY, the repository itself (which also includes code) seems to have no license file.
I am not sure if CC BY would be a good idea also here, or if maybe MIT would be better.

[uekerman]

There is https://github.com/precice/precice.github.io/blob/master/licenses/LICENSE, which we probably need to update

[MakisH]

I am reopening this issue, as the license is still rather implicit.

In the Jekyll version, we include the licenses of documentation-theme-jekyll (MIT, Copyright of the creator) and Navgoco jQuery component (BSD 3-clause, Copyright of the creator).

In the README we clearly specify CC-BY 4.0 for the content.

In the Hugo version (#979), we inherit the Apache 2.0 license, without Copyright identification.

For the technical aspects of the website, we should make the license clearer. In Jekyll, I would assume MIT, with a similar notice as the content (The preCICE Developers - precice.org).

Since some files could be extracted from this repository (e.g., plugins), we should add REUSE/SPDX headers to the relevant files. Since Apache 2.0 and MIT are, to my knowledge, compatible, it does not really matter which of the two we add. For continuity and simplicity (in this project we mainly would welcome attribution, if anything), MIT might be better.

If there are no objections or further comments, I will prepare a PR with some statements and SPDX headers.