Add README.md

README.md

+Ultrasonic Multipath Propagation Model
+
+- Model is given as Matlab class in file: ./forward_model/us_mp_model.m
+- Usage:
+
+`addpath('./lib/cosa-tools-matlab/lib');
+
+%% gen model with properties
+us_mp_mdl = us_mp_model(6e-2, ...     %d1
+                        6e-2, ...     %d2
+                        6e-3, ...     %b
+                        90e3, ...     %f_low 
+                        150e3, ...    %f_high 
+                        92.71e-6, ... %T_pulse
+                        13.5e-2, ...  % d_refl
+                        0.15);        % R
+d_los = 0:2e-4:12e-2;
+for idx = 1:length(d_los)
+    [f, y] = us_mp_mdl.get_rx_db(d_los(idx));
+    plot(f, y);
+end`