added some helper message to lte-softmodem

targets/RT/USER/lte-softmodem.c

@@ -383,6 +383,7 @@ void help (void) {
   printf("  --ue-scan_carrier set UE to scan around carrier\n");
   printf("  --loop-memory get softmodem (UE) to loop through memory instead of acquiring from HW\n");
   printf("  --mmapped-dma sets flag for improved EXMIMO UE performance\n");  
+  printf("  --single-thread runs lte-softmodem in only one thread\n"); 
   printf("  -C Set the downlink frequency for all component carriers\n");
   printf("  -d Enable soft scope and L1 and L2 stats (Xforms)\n");
   printf("  -F Calibrate the EXMIMO borad, available files: exmimo2_2arxg.lime exmimo2_2brxg.lime \n");