cli/load_data examples for -l option

Author: yuankailiu

src/mintpy/cli/load_data.py

@@ -49,7 +49,11 @@
 
   # load geometry ONLY
   smallbaselineApp.py SaltonSeaSenDT173.txt -g
-  load_data.py -t smallbaselineApp.cfg --geom
+  load_data.py -t smallbaselineApp.cfg -l geom
+
+  # load ionoshpere time series ONLY
+  smallbaselineApp.py SaltonSeaSenDT173.txt -g
+  load_data.py -t smallbaselineApp.cfg -l ion
 """