Improve documentation for Kw parameterisations

[lukegre]

Currently, each of the kw parameterisations has basic documentation (article + wind product).

More detail in the documentation would help the users understand when to use a particular parameterisation. Further, the method used to arrive at the estimate could be helpful.

Lastly, a dedicated page briefly outlining the theory of gas transfer velocity and when to use which product would be immensely useful. Perhaps a table showing the wind product used for a parameterisation.