Add more documentation on how to connect dApps to smart contracts.

**Description**
In the documentation, we have some explanations on how to compile dApps and there are links to some examples, but there is no step-by-step guide on how to write a dApps. In particular, it is not clear how to obtain a schema that is encoded properly to be used in the dApp to pass parameters to functions. It would be nice to add a more in-depth tutorial that covers everything.