🚒 switched to pip-compile

[stevejpurves]

Whilst working on the submission documentation.

I've been reviewing how we should recommend people provide pinned dependencies and in this PR have switched to using pip-compile along with requirements.in and am suggesting for the MVP that we ask people to use pip alone for the submissions rather than pip or conda.

Happy to expand that as needed though, as there is a different workflow that can be achieved with conda although a little more clunkly.

Proposal is we make the templates pip/pip-compile first.

and a question is should we support (additional automated checks) and document a second supported conda route for people?