Upgrade description.md in docs

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• add model versions

• move images to docs/images

  • Links in the README.md

    ![Nice plot](./docs/images/myimage.png)

• Add references:

  • Carton, J. A., Chepurin, G., Cao, X., and Giese, B. 2000. A simple ocean data assimilation analysis of the global upper ocean 1950–95. Part I: methodology. Journal of Physical Oceanography, 30: 294–309.

  • Carton, J. A., and Giese, B. S. 2008. A reanalysis of ocean climate using Simple Ocean Data Assimilation (SODA). Monthly Weather Review, 136: 2999–3017.