Added subpage for import mechanism

Author: SundermannC

language/Submodels.md

@@ -0,0 +1,48 @@
+### Importing Submodels
+
+Larger variability models may be hard to overview. To simplify viewing and editing such models, UVL allows specifying submodels that can then be referenced in a composing model.
+
+Consider our sandwich model as example:
+
+<code>
+<b>features</b>
+    Sandwich
+        <b>mandatory</b>
+            Bread
+        <b>optional</b>
+            Sauce
+                <b>alternative</b>
+                    Ketchup
+                    Mustard
+            Cheese
+<b>constraints</b>
+    Ketchup => Cheese
+</code>
+
+Here, it may make sense to decompose the Sauce into a separate UVL model:
+
+<code>
+<b>features</b>
+    Type
+        <b>alternative</b>
+            Ketchup
+            Mustard
+</code>
+
+Suppose we stored this submodel in a path ./submodels/Sauces.uvl
+
+We can then use this submodel by using the **imports** keyword in a composed model. Further, we can reference the root feature of the imported model at any point the feature tree.
+
+<code>
+<b>imports</b>
+    submodels.Sauces as Sauce
+
+<b>features</b>
+    Sandwich
+        <b>mandatory</b>
+            Bread
+        <b>optional</b>
+            Sauce.Type
+<b>constraints</b>
+    Sauce.Ketchup => Cheese
+</code>