Fix typo

Author: jakejscott

src/doc/guide-pointers.md

@@ -655,7 +655,7 @@ This part is coming soon.
 # Returning Pointers
 
 In many languages with pointers, you'd return a pointer from a function
-so as to avoid a copying a large data structure. For example:
+so as to avoid copying a large data structure. For example:
 
 ```{rust}
 struct BigStruct {