bbim docs: add user interface subsection, general workspace

src/blenderbim/docs/users/general_usage.rst

@@ -9,4 +9,5 @@ and exploring models.
    :maxdepth: 1
    :caption: Contents:
 
+   general_usage/interface
    general_usage/ifc_project

src/blenderbim/docs/users/general_usage/interface.rst

@@ -0,0 +1,11 @@
+User Interface
+==============
+
+This section covers the general user interface of BlenderBIM.
+
+.. toctree::
+   :hidden:
+   :maxdepth: 1
+   :caption: Contents:
+
+   interface/workspace

src/blenderbim/docs/users/general_usage/interface/workspace.rst

@@ -0,0 +1,27 @@
+Workspace
+=========
+
+For general informations about the Blender user interface see the respective 
+`Blender handbook section <https://docs.blender.org/manual/en/latest/interface/index.html>`__.
+
+After installation of BlenderBIM the default Blender start-up screen looks different from the standard Blender interface.
+
+BlenderBIM adds a new `BIM` **Workspace** to the interface and by default activates this workspace on start-up.
+It also modifies the layout of views and sidebars and adds custom functionality to the toolbar.
+The left **Outliner** panel shows a tree of geometric objects. The centre main **Viewport** panel shows 3D geometry.
+The right **Properties** panel shows data and relationships.
+
+.. image:: images/interface_window_start-up.png
+   :alt: Blender start up window with installed BlenderBIM add-on
+
+1. BlenderBIM `BIM` workspace tab
+2. Outliner with the document tree
+3. Main 3D viewport
+4. Property editor
+5. Toolbar with added BIM functionality
+6. Status bar with information about the currently used Blender and BlenderBIM version
+
+Additionally, the `File` menue in the Topbar adds menue entries to Create/Open and Save an IFC project directly.
+
+.. image:: images/interface_window_file-menue.png
+   :alt: Additional file menue options related to IFC projects