Fix Recommended Folder Structure section

[kakysha]

Right now the Building Modules > Recommended Module Structure advocates to put all type definitions into root module folder, while this is almost never possible due to circular references between module package and keeper package (module.go in root package needs reference to keeper, and keeper needs references to almost all module types defined in root package).
Besides that, never seen any module that follows these pattern, I suppose exactly due to this reason. All modules keep using separate types package instead of placing type definitions inside root folder.

[julienrbrt]

x/group and x/nft follow it.
But that's true that it is not being followed by all modules.

However if you follow it you still do not have circular dependencies as you have a keeper and a module package.

[julienrbrt]

For reference: #17657 (comment)