main: comment the meaning of init_SBR

src/main.cpp

@@ -533,8 +533,12 @@ int main(int argc, char **argv) {
 
 						}else{
 
-							if(init_SBR)
+							if(init_SBR) {
+								// This is legacy code kept for a potential future (and more generic ?) use:
+								// warm start the branch-and-bound with a "good" upper bound at the root node,
+								// generally obtained thanks to some l0 heuristic.
 								x0.load(pathdata_x0_sbr_2p0.str(), raw_ascii);
+							}
 							born_sup = pow(norm(y- A*x0, 2), 2) + lambda(0) * norm_zero(x0, exp10(-4)) - norm2carre_y;
 							cout << "born_sup : "<< born_sup << endl;