:book: add docs about dnt 💗 monorepo

[Gaubee]

Add documentation describing how to compile Monorepo-style projects with dnt.

[wKich]

@Gaubee, thanks for explaining how to build npm packages in Deno monorepo. But according to your example, you are using import_map.npm.json for importMap, so if I also have imports in deno.json it seems there is no simple way to combine both maps together, right?

I don't see version resolving for packages described in import_map.npm.json. Is built package always depends on the latest version, because there is no version specified in the import map? Hm... it is. Which actually really bad behaviour that might break old version packages.

I wonder, why dnt can't resolve imports from a deno workspace configuration without need to adding complexity to a project