Provide more context in code example

blog/content/second-edition/posts/10-paging-implementation/index.md

@@ -445,10 +445,17 @@ We see that there are various non-empty entries, which all map to different leve
 To traverse the page tables further and take a look at a level 3 table, we can take the mapped frame of an entry convert it to a virtual address again:
 
 ```rust
+// in the for loop in src/main.rs
+
+use x86_64::{structures::paging::PageTable, VirtAddr};
+
+if !entry.is_unused() {
+    println!("L4 Entry {}: {:?}", i, entry);
+
     // get the physical address from the entry and convert it
     let phys = entry.frame().unwrap().start_address();
     let virt = phys.as_u64() + boot_info.physical_memory_offset;
-let ptr = VirtAddr::new(virt).as_mut_ptr()
+    let ptr = VirtAddr::new(virt).as_mut_ptr();
     let l3_table: &PageTable = unsafe { &*ptr };
 
     // print non-empty entries of the level 3 table
@@ -457,6 +464,7 @@ for (i, entry) in l3_table.iter().enumerate() {
             println!("  L3 Entry {}: {:?}", i, entry);
         }
     }
+}
 ```
 
 For looking at the level 2 and level 1 tables, we repeat that process for the level 3 and level 2 entries. As you can imagine, this gets very verbose quickly, so we don't show the full code here.