Use of tin-foil BCs specified

in both .rst and .pdf manual. Sentence about epsilon_r rephrased

modules/DL_MESO_DPD/dipole_dlmeso_dpd/readme.rst

@@ -64,10 +64,9 @@ The Kirkwood number for a pure system is
 :math:`g_k=\frac{\langle\vec{P}^2\rangle}{N_{mol}\langle \vec{p}^2\rangle}`,
 where :math:`\langle\dots\rangle` indicates an average over trajectories.
 If the dipoles' orientations are not correlated, then :math:`g_k\simeq 1`.
-Also, an estimate for the relative dielectric permittivity of the medium is obtained from linear response
+Also, the relative dielectric permittivity of the medium is calculated from linear response
 theory: :math:`\epsilon_r= 1 + \frac{4 \pi}{3} l_B \frac{\langle\vec{P}^2\rangle}{V}`,
-where :math:`l_B` is Bjerrum length.
-
+where :math:`l_B` is Bjerrum length and tin-foil boundary conditions are used.
 
 Background Information
 ______________________