Update docs/source/background/why-cset.rst

Co-authored-by: James Frost <[email protected]>

docs/source/background/why-cset.rst

@@ -4,7 +4,7 @@ Why use CSET?
 When evaluating weather and climate models we are trying to understand the
 characteristics of our model configurations, the physical processes that lead
 to biases, and how they compares to other models (physical and machine learned),
-model configurations and observations. This can be a very iterative process, and
+model configurations and observations. This is an iterative process, and
 each step of evaluation unveils more questions that need investigations.
 Evaluation often follows an individual approach by researchers spending
 significant resource on scientific and technical development.