architecture.md: fix the header size

docs/architecture.md

@@ -25,7 +25,7 @@ struct passwd {
 Turbonss, among others, implements this call, and takes the following steps to
 resolve a username to a `struct passwd*`:
 
-- Open the DB (using `mmap`) and interpret it's first 64 bytes as a `*struct
+- Open the DB (using `mmap`) and interpret it's first 128 bytes as a `*struct
   Header`. The header stores offsets to the sections of the file. This needs to
   be done once, when the NSS library is loaded.
 - Hash the username using a perfect hash function. Perfect hash function