Update swapchain.md

add period between sentences

tutorial/book/src/presentation/swapchain.md

@@ -321,7 +321,7 @@ Next, we need to specify how to handle swapchain images that will be used across
 * `vk::SharingMode::EXCLUSIVE` – An image is owned by one queue family at a time and ownership must be explicitly transferred before using it in another queue family. This option offers the best performance.
 * `vk::SharingMode::CONCURRENT` – Images can be used across multiple queue families without explicit ownership transfers.
 
-If the queue families differ, then we'll be using the concurrent mode in this tutorial to avoid having to do the ownership chapters, because these involve some concepts that are better explained at a later time. Concurrent mode requires you to specify in advance between which queue families ownership will be shared using the `queue_family_indices` builder method If the graphics queue family and presentation queue family are the same, which will be the case on most hardware, then we should stick to exclusive mode, because concurrent mode requires you to specify at least two distinct queue families.
+If the queue families differ, then we'll be using the concurrent mode in this tutorial to avoid having to do the ownership chapters, because these involve some concepts that are better explained at a later time. Concurrent mode requires you to specify in advance between which queue families ownership will be shared using the `queue_family_indices` builder method. If the graphics queue family and presentation queue family are the same, which will be the case on most hardware, then we should stick to exclusive mode, because concurrent mode requires you to specify at least two distinct queue families.
 
 ```rust,noplaypen
 let mut queue_family_indices = vec![];