doc: small grammar fix

src/doc/complement-design-faq.md

@@ -95,7 +95,7 @@ code should need to run is a stack.
 `match` being exhaustive has some useful properties. First, if every
 possibility is covered by the `match`, adding further variants to the `enum`
 in the future will prompt a compilation failure, rather than runtime panic.
-Second, it makes cost explicit. In general, only safe way to have a
+Second, it makes cost explicit. In general, the only safe way to have a
 non-exhaustive match would be to panic the task if nothing is matched, though
 it could fall through if the type of the `match` expression is `()`. This sort
 of hidden cost and special casing is against the language's philosophy. It's