Typo fix in readme

Author: dvalters

readme.md

@@ -4,7 +4,7 @@ This is the development version of the HAIL-CAESAR model.
 
 HAIL-CAESAR is a hydrodynamic, landscape evolution, cellular automaton model. In other words, it simulates hydrological and erosional processes in a rive catchment, for the purposes of investigating flood-inundation, sediment transport and catchment evolution over a range of timescales from hours to thousands of years. (And potentially longer if you are really patient enough...)
 
-The model is derived from the [CAESAR-Lisflood model](https://sourceforge.net/projects/caesar-lisflood/), which a C#/.NET Windows-based implementation of the model, with a very useful GUI. (HAIL-CAESAR doesn't do GUIs and is designed for linux or command line use.)
+The model is derived from the [CAESAR-Lisflood model](https://sourceforge.net/projects/caesar-lisflood/), which is a C#/.NET Windows-based implementation of the model, with a very useful GUI. (HAIL-CAESAR doesn't do GUIs and is designed for linux or command line use.)
 
 (Documentation can be found here](http://lsdtopotools.github.io/LSDTT_book/#_hydrological_and_erosion_modelling). (Part of the @LSDTopoTools documentation). I may one-day write some separate documentation.