[Doc] Add explanation for sites in its own file

[bobot]

No description provided.

[bobot]

I would like to test the code written as example, I wanted to use literalinclude but it is never used in the documentation. Should I avoid it?

[ghost]

In the long term, we'd like to use the tools developed by the community for that. odoc and mdx to be precise. So it seems better to me to wait for these to be ready, which shouldn't be too long now.

[bobot]

Ok. Do you think the added documentation is enough?

[ghost]

I haven't looked at the whole documentation so far, but looking at the beginning I feel like we are missing a gentle introduction. The documentation goes directly from "How to load additional files at runtime" to "Sites" and some technical difficulty.

I'd start the page with a small discussion about the fact that there are many ways for applications to load files at runtime and Dune provides a well tested, key-in-hand portable system for doing so. Then explain that the model works by defining "sites" where files will be installed and looked up at runtime. The discussion about the main difficulty should come much later IMO. It's more an implementation difficulty. It's worth explaining, but it's more aimed at users who would like to go further and understand how the system works. You don't need to know about it to use the system for instance.