Add license

[colinsauze]

• adds a LICENSE file
• adds a Copyright and license statement to every source file, jupyter notebook and config
• adds a Copyright and license statement to the README
• adds a CONTRIBUTING.md and CITATION.cff file

In the CITATINON.cff I have tried to include everybody who has actively contributed to this project, including those who have not contributed code but have provided advice, testing and pre-existing code examples that have been converted to python and incorporated.

@Klankers is missing a ORCID in the CITATION file.

For the copyright statement I have used "National Oceanography Centre and Contributors" @callumrollo @Klankers is this acceptable to you? or would you prefer we reference VOTO explicitly here?

[callumrollo]

That sounds great Colin. we're not overly concerned about recognition for VOTO, just wanted to get some form of FOSS license in place to ensure we're using and adapting the code in the appropriate way moving forward

[colinsauze]

fixes #94

[Obsidian500]

Thanks for this Colin!