Update README.md

fixed typo

Author: brettin

examples/histogen/README.md

@@ -2,7 +2,7 @@
 
 ## Usage
 
-The CANDLE-ized versions of the codes can simply be run without any command line arguments, with the default settings being read from the corresponding `default_mode`l file.
+The CANDLE-ized versions of the codes can simply be run without any command line arguments, with the default settings being read from the corresponding `default_model` file.
 When needed, the CANDLE versions also use the `fetch_file` methods, which store the data in the top-level `Data/Examples` directory.
 Any keywords in the `default_model` file can be overwritten with the appropriate command line argument.
 The orginal codes and workflow below are preserved for comparison.