update doc/en structure

doc/en/block-models.md

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+# Block Models
+
+Block model may be created with following properties:
+
+```js
+"model": "custom",
+"model-primitives": {
+    "aabbs": [
+	    // list of AABB primitives
+    ],
+    // ... other primitives
+}
+```
+
+**AABB** primitive is an array of values:
+```
+[x, y, z, width, height, depth, texture names for all 6 sides]
+```
+
+**tetragon** primitive (more like parallelogram) an array of three vectors, describing primitive position, X vector \* width, Y vector \* height.