Explain module aliases in module tutorial

[cuihtlauac]

Add text in the module tutorial explaining that kind of code:

module Foo = Foo
module Bar = Baz
module Qux = Set.Make(Quy)

Module tutorial PR: #1778

https://v2.ocaml.org/releases/5.1/htmlman/modules.html

[The-Amoghavarsha]

It would be helpful if you provided the location with a full path, such as data/tutorials/getting-started (For other issues as well).