ts/wf/teseco [TASK]: add a note regarding gaps to usage information

src/ts/wf/teseco.cc

@@ -88,6 +88,10 @@ int main(int iargc, char* argv[])
     "pressure correction or magentic field correction may be applied" "\n"
     "to seismic recordings." "\n"
     "\n"
+    "All input traces (all traces in signal and correction files) are\n"
+    "expected to cover the same time window. This program is not able\n"
+    "to handle time series containing gaps properly.\n"
+    "\n"
     "outfile      output filename" "\n"
     "signal       signal filename (multiple traces may be selected;\n"
     "             each correction will be applied to each of them)\n"