[doc] Update parallel model creation workflow.

web/content/docs/tools/workflows/create-a-simple-parallel-model/index.pandoc

@@ -41,12 +41,30 @@ where `a`, `b`, and `c` should be choosen according to the needs.
 |  422  |  422  |  422  | ~ 75.15 | 240 | yes |
 |  465  |  465  |  465  | ~ 100.54 | 320 | |
 
+
+For the boundary conditions, if they are simple (_i.e._ homogeneous), the
+simplest `.gml` file is sufficient for the serial case, but for heterogeneous
+boundary conditions and parallelization boundary mesh files are needed. There
+are two possibilities to create such files:
+
+ - If there is a `.gml` file, use [`constructMeshesFromGeometry`
+   tool](../../model-preparation/constructmeshesfromgeometry/), which takes the
+   mesh file and geometry and creates all the boundaries which are named in the
+   `.gml` file with the required `bulk_node_ids` and `bulk_element_ids`
+   mappings.
+ - If there is a boundary mesh (generated by gmsh or salome, or extracted in
+   paraview, for example) use the [`identifySubdomains`
+   tool](../../model-preparation/identifysubdomains/) to create or verify the
+   needed `bulk_node_ids` and `bulk_element_ids` mappings.
+
 ## Partition the mesh
 
 Convert vtu mesh into metis input mesh
 ```bin/partmesh -i cube_1x1x1_hex_axbxc.vtu --ogs2metis```
-=> results in a file cube_1x1x1_hex_axbxc.mesh
-```bin/partmesh -n number_of_partitions -m -i cube_1x1x1_hex_axbxc```
+=> results in a file `cube_1x1x1_hex_axbxc.mesh`
+Then partition the mesh and the corresponding boundaries.
+```bin/partmesh -n number_of_partitions -m -i cube_1x1x1_hex_axbxc.vtu -- boundary_meshes*.vtu```
+This will result in a bunch of `.bin` files.
 
 ## Deciding the part to benchmark