[WIP] Cuboid feature user guide (#1218)

* Initial cuboid description

* Added Gifs

* Added gifs  to descriptions

* Formatting fixes

* Codacy Fixes

cvat/apps/documentation/user_guide.md

@@ -28,6 +28,7 @@
   - [Annotation with box by 4 points](#annotation-with-box-by-4-points)
   - [Annotation with polygons](#annotation-with-polygons)
   - [Annotation with polylines](#annotation-with-polylines)
+  - [Annotation with cuboids](#annotation-with-cuboids)
   - [Annotation with points](#annotation-with-points)
     - [Points in annotation mode](#points-in-annotation-mode)
     - [Linear interpolation with one point](#linear-interpolation-with-one-point)
@@ -1017,6 +1018,62 @@ automatically. You can adjust the polyline after it has been drawn.
 
 ![](static/documentation/images/image039.jpg)
 
+## Annotation with cuboids
+
+It is used to annotate 3 dimensional objects such as cars, boxes, etc... 
+Currently the feature supports one point perspective and has the contraint
+where the vertical edges are exactly parallel to the sides. 
+
+### Creating the cuboid
+
+Before starting, you have to be sure that ``Cuboid`` is selected.
+
+Press ``N`` for entering drawing mode. There are many ways to draw a cuboid.
+You may draw the cuboid by placing 4 points, after which the drawing completes automatically.
+The first 3 points will represent a plane of the cuboid
+while the last point represents the depth of that plane.
+For the first 3 points, it is recomended to only draw the 2 closest side faces,
+as well as the top and bottom face. 
+
+A few examples:  
+![](static/documentation/images/CuboidDrawing1.gif)
+
+![](static/documentation/images/CuboidDrawing2.gif)
+
+![](static/documentation/images/CuboidDrawing3.gif)
+
+### Editing the cuboid
+
+The cuboid can be edited in multiple ways, by dragging points or by dragging certain faces. 
+First notice that there is a face that is painted with pink lines only, let us call it the front face. 
+
+The cuboid can be moved by simply dragging the shape as normal. 
+The cuboid can be extended by dragging on the point in the middle of the edges. 
+The cuboid can also be extended up and down by dragging the point at the vertices. 
+
+![](static/documentation/images/CuboidEditing1.gif)
+
+To draw with perpective effects it is assumed that the front face is the closest to the camera.
+To begin simply drag the points on the vertices that are not on the pink/front face while holding ``Shift``.
+The cuboid can then be edited as usual.
+
+![](static/documentation/images/EditingPerspective.gif)
+
+If you wish to reset perspective effects, you may right click on cuboid,
+and select ``Reset Perspective`` to return to a regular cuboid. 
+
+The location of the pink face can be swapped with the adjacent visible side face.
+This is done by right clicking on the cuboid and selecting ``Switch Perspective Orientation``.
+Note that this will also reset the perspective effects. 
+
+![](static/documentation/images/ResetPerspective.gif)
+
+Certain faces of the cuboid can also be edited,
+these faces are the left, right and dorsal faces, relative to the pink face. 
+Simply drag the faces to move them independently from the rest of the cuboid. 
+
+![](static/documentation/images/CuboidEditing2.gif)
+
 ## Annotation with points
 
 ### Points in annotation mode