rewording

Author: willmcgugan

docs/guide/reactivity.md

@@ -167,9 +167,9 @@ If you click the buttons in the above example it will show the current count. Wh
 
 Watch methods are another superpower.
 Textual will call watch methods when reactive attributes are modified.
-Watch methods begin with `watch_` followed by the name of the attribute.
-If the watch method accepts a positional argument, it will be called with the new assigned value.
-If the watch method accepts *two* positional arguments, it will be called with both the *old* value and the *new* value.
+Watch method names begin with `watch_` followed by the name of the attribute, and should accept one or two arguments.
+If the method accepts a single argument, it will be called with the new assigned value.
+If the method accepts *two* positional arguments, it will be called with both the *old* value and the *new* value.
 
 The following app will display any color you type in to the input. Try it with a valid color in Textual CSS. For example `"darkorchid"` or `"#52de44"`.