Improve the documentation a bit

examples/Modules/Main.dbl

@@ -4,19 +4,24 @@
     ```
     /
     ├─ Main
-    │  ├─ Main (this file)
-    │  ├─ A
+    │  ├─ Main      (this file)
+    │  ├─ A         (imports B/C/D, resolving to /Main/B/C/D)
     │  ├─ B
     │  │  ├─ A
     │  │  └─ C
-    │  │      └─ D
+    │  │      └─ D  (imports A, resolving to /Main/B/A)
     │  └─ C
     ├─ List
     ⋮
     ```
     Modules under `/Main/` are local to this example and follow its directory
     structure. Additionaly, the module `/List` from the standard library is
-    imported. *)
+    imported.
+
+    Relative imports refer to the module which is the closest to the importing
+    module, working upwards through the hierarchy. In this example the module
+    `/Main/B/C/D` imports the relative path `A`, and the nearest matching
+    module is `/Main/B/A`. *)
 
 import List
 

src/Parser/Import.ml

@@ -70,9 +70,13 @@ let find_mod prefix (p : Raw.import_path) =
   | IPRelative(p, n) -> find_mod_rel prefix (p, n)
 
 (** Find and parse imported module relative to the path [prefix] and add it
-    to the [mods] map with the absolute mod identifier as the key.
+    to the module graph [mods] with the absolute mod identifier as the map key.
+    Each vertex in the map stores a list of definition and the module's
+    dependencies (graph edges).
+
     Previously imported modules can be passed in the [imported] parameter
-    to avoid including them twice. *)
+    to avoid including them twice. These modules will not be added to the
+    graph, but edges from other vertices may point to them. *)
 let rec parse_import ~imported prefix mods (import : Raw.import) =
   let path, new_name =
     match import.data with