docs: clarify cookie domain normalization (#17590)

docs/api/cookies.md

@@ -107,7 +107,7 @@ with `callback(error, cookies)` on complete.
   * `url` String - The url to associate the cookie with.
   * `name` String (optional) - The name of the cookie. Empty by default if omitted.
   * `value` String (optional) - The value of the cookie. Empty by default if omitted.
-  * `domain` String (optional) - The domain of the cookie. Empty by default if omitted.
+  * `domain` String (optional) - The domain of the cookie; this will be normalized with a preceding dot so that it's also valid for subdomains. Empty by default if omitted.
   * `path` String (optional) - The path of the cookie. Empty by default if omitted.
   * `secure` Boolean (optional) - Whether the cookie should be marked as Secure. Defaults to
     false.

docs/api/structures/cookie.md

@@ -2,8 +2,8 @@
 
 * `name` String - The name of the cookie.
 * `value` String - The value of the cookie.
-* `domain` String (optional) - The domain of the cookie.
-* `hostOnly` Boolean (optional) - Whether the cookie is a host-only cookie.
+* `domain` String (optional) - The domain of the cookie; this will be normalized with a preceding dot so that it's also valid for subdomains.
+* `hostOnly` Boolean (optional) - Whether the cookie is a host-only cookie; this will only be `true` if no domain was passed.
 * `path` String (optional) - The path of the cookie.
 * `secure` Boolean (optional) - Whether the cookie is marked as secure.
 * `httpOnly` Boolean (optional) - Whether the cookie is marked as HTTP only.