Membranes Section

[membranes] - contains information about membranes
a b c

where:
a = index to particle 1 of membrane triangle
b = index to particle 2 of membrane triangle
c = index to particle 3 of membrane triangle

Membranes are comprised of triangles with 3 particles as their vertex positions.
The indicies refer to the order in which particles are listed in the [positions]
section.