Update man.Rmd (#1084)

Grammatical fix

man.Rmd

@@ -711,7 +711,7 @@ Instead, you'll need to do it by hand.
 If you can avoid doing something that must then be undone, that is the best way to go and this is especially true for examples.
 
 These constraints are often in tension with good documentation, if you're trying to document a function that somehow changes the state of the world.
-For example, you have to "show your work", i.e. all of your code, which means that your users will see all of the setup and teardown, even it is not typical for authentic usage.
+For example, you have to "show your work", i.e. all of your code, which means that your users will see all of the setup and teardown, even if it is not typical for authentic usage.
 If you're finding it hard to follow the rules, this might be another sign to switch to a vignette (see @sec-vignettes).
 
 ::: callout-warning