Add preprocessing sections to the different driver docs

[Huite]

The current MetaMod coupler documentation section mentions:

• Configuration
• Technical reference
• Example

I think it makes a lot of sense to have another section called "preprocessing". This is obviously relevant to most users, as they will be quite involved with the spatial coupling logic (making sure models align for example).

Such a document should introduce the primod package, explain the requirements before a model can be coupled in terms of its schematization and concepts, mention how the automatic definition is exchanges is done (based on spatial locations), as well as mention the relevant components of all models. A full example is not required, but for readability, some duplication might be desirable.