chore: Move placeholder figure to methods

There are still a couple of figures in the methods chapter. This breaks
it's use elsewhere.

ref #83

00_Introduction/introduction.md

@@ -137,7 +137,9 @@ replicating experimental results.
 The Lewis--Wahnström model displays the same two-step relaxation process [@Wahnstrom1993,@Wahnstrom1997,@Lombardo2006]
 that is characteristic of fragile liquids in experiments.
 
-![The geometry of the Lewis--Wahnström model](../placeholder_figure.png){width=80% #fig:lewis_wahnstrom_mol}
+![The geometry of the Lewis--Wahnström model.
+There is an angle of \SI{75}{\degree} subtending the centers of the thee particles.
+](../00_Introduction/figures/lewis_wahnstrom.svg){width=80% #fig:lewis_wahnstrom_mol}
 
 The Lewis--Wahnström model of ortho-terphenyl is the most widely studied
 computational model of ortho-terphenyl,

01_Methods/Simulation_Conditions.md

@@ -244,9 +244,9 @@ were packed together
 
 :::{class=subfigures id=fig:crystal_unit_cell}
 
-![p2](../placeholder_figure.png){width=33% #fig:crystal_unit_cell_p2}
-![pg](../placeholder_figure.png){width=33% #fig:crystal_unit_cell_pg}
-![p2gg](../placeholder_figure.png){width=33% #fig:crystal_unit_cell_p2gg}
+![p2](../01_Methods/figures/placeholder_figure.png){width=33% #fig:crystal_unit_cell_p2}
+![pg](../01_Methods/figures/placeholder_figure.png){width=33% #fig:crystal_unit_cell_pg}
+![p2gg](../01_Methods/figures/placeholder_figure.png){width=33% #fig:crystal_unit_cell_p2gg}
 
 The unit cells of the p2 (a) the pg (b) and the p2gg (c) crystals
 documenting the unit cell parameters
@@ -308,7 +308,7 @@ of the number of overall layers
 so the orthorhombic configuration is favourable.
 
 ![Depicting conversion of tilted cell to orthorhombic
-](../placeholder_figure.png){width=80% #fig:orthorhombisation}
+](../01_Methods/figures/placeholder_figure.png){width=80% #fig:orthorhombisation}
 
 The outer 1/3 of the orthorhombic configuration is then melted
 at 2.2 times the melting point,