typo fix; closes #64

src/2_debye_model.md

@@ -182,7 +182,7 @@ $$
 
 We can trace back all the factors in the density of states to their origin:
 
-* $(L/2\pi)^3$ is the volume per allowed wave in the reciprocal space
+* $(L/2\pi)^3$ is the number of possible waves per unit volume in the reciprocal space
 * $4π$ is the area of a unit sphere, the result of integration over $d \varphi$ and $dθ$
 * $ω^2$ is due to the area of this sphere being proportional to its squared radius
 * $3$ is the number of possible polarizations in 3D