Processed Wijtze Pieter's review comments

Clarified the opposite orientation of the geometry's second edge.

applications/GeoMechanicsApplication/custom_geometries/README.md

@@ -17,4 +17,4 @@ Similarly, the 3+3 line interface geometry has the following node numbering for
 
 One thing to note, is that this line interface geometry does not implement functions from the Geometry base class which are related to the integration scheme. That is because most of the time, interface geometries are used with a Lobatto integration scheme, which is not supported by the Geometry base class.
 
-Any line interface geometry has two edges. The first edge coincides with the first side (i.e. bottom side in the above figures) of the geometry. The first edge's nodes are identical to the nodes at the first edge. For the 3+3 line interface geometry this means the list of node IDs equals [1, 2, 3]. The second edge references the nodes of the second side (i.e. top side in the above figures) of the line interface geometry. However, this edge traverses the second side in opposite direction. This implies that the end nodes will be swapped and any high-order nodes are reversed. For instance, for the 3+3 line interface geometry the second edge's nodes are ordered as follows: [5, 4, 6];
+Any line interface geometry has two edges. The first edge coincides with the first side (i.e. bottom side in the above figures) of the geometry. The ordering of the first edge's nodes is identical to the one of the first side. For the 3+3 line interface geometry this means the list of node IDs equals [1, 2, 3]. The second edge references the nodes of the second side (i.e. top side in the above figures) of the line interface geometry. However, this edge has opposite orientation compared to the side, and therefore a node numbering according to the opposite direction. With respect to the node numbering of the side, this implies that the end nodes will be swapped and any high-order nodes are reversed. For instance, for the 3+3 line interface geometry the second edge's nodes are ordered as follows: [5, 4, 6];