Update text.md

The sentence "Often, some parts of a component's state need to be computed from other parts (such as a fullname derived from a firstname and a lastname), and recomputed whenever they change." was very confusing and also grammatically incorrect because "and recomputed whenever they change" is a dependent clause.

According to Grammarly, "A dependent clause is a clause that cannot stand as a sentence in its own right, such as before I left the parking lot. When a complex sentence contains a dependent clause like this one, a comma is not used unless the dependent clause comes before the independent clause."

https://www.grammarly.com/blog/comma-in-complex-sentences/#:~:text=A%20dependent%20clause%20is%20a,comes%20before%20the%20independent%20clause.

site/content/tutorial/02-reactivity/02-reactive-declarations/text.md

@@ -2,7 +2,7 @@
 title: Declarations
 ---
 
-Svelte automatically updates the DOM when your component's state changes. Often, some parts of a component's state need to be computed from *other* parts (such as a `fullname` derived from a `firstname` and a `lastname`), and recomputed whenever they change.
+Svelte automatically updates the DOM when your component's state changes. Often, some parts of a component's state depends on *other* parts. For example, you may want to have `fullname` derived from `firstname` and `lastname` and also want to recompute `fullname` when `firstname` and/or `lastname` changes. 
 
 For these, we have *reactive declarations*. They look like this: