Document repository licensing options

[StevenMaude]

Currently, there is an MIT licence included in the template. That, presumably, is the licence under which we distribute this template.

Researchers then continue to implicitly use that licence for their own contributions, even if not an explicit opted-in decision:

• the licence is included when a new repository is created from this template;
• GitHub also declare that the new repository has this licence, from when the new repository is created.

However, a researcher may want to use the sublicense right granted by the MIT licence, and may not be aware that these rights exists.

It might be preferable to state, somewhere, something along the lines of:

• The OpenSAFELY template repository has a MIT licence.
• The MIT license does give you the right to sublicense our work under a different licence of your choice (providing the original license and copyright notice is still included, please see the license)
• We encourage you to share your OpenSAFELY study code under a permissive open source licence so that others can benefit reuse.