Added a tex file for the equations of pair rounded/polygon and rounded/polyhedron

doc/src/Eqs/pair_body_rounded.tex

+\documentstyle[12pt]{article}
+
+\begin{document}
+
+\begin{eqnarray*}
+ F_n &=& k_n \delta_n - c_n v_n, \qquad \delta_n \le 0 \\
+     &=& -k_{na} \delta_n - c_n v_n, \qquad 0 < \delta_n \le r_c \\
+     &=& 0 \qquad \qquad \qquad \qquad \delta_n > r_c \\
+ F_t &=& \mu k_n \delta_n - c_t v_t, \qquad \delta_n \le 0 \\
+     &=& 0 \qquad \qquad \qquad \qquad \delta_n > 0
+\end{eqnarray*}
+
+\end{document}