Clarify GPT hidden flag design

wiki/src/contribute/design/installation.mdwn

@@ -47,7 +47,7 @@ Partitioning
 
 The storage device is partitioned using [GPT](https://en.wikipedia.org/wiki/GUID_Partition_Table). Using GPT has several desirable properties:
 
- * The system partition can be hidden from Windows. Hopefully this
+ * The system partition is hidden from Windows using the `hidden` flag of GPT. Hopefully this
    should prevent some misuse of Tails system partition, even if we
    explicitly discourage users to plug their Tails USB stick to a
    running system (Windows among other OS).