docs: minor update

boot/intro.txt

@@ -3,6 +3,10 @@ File: Introduction
 Section: Legacy
 
 >
+> +------------+  multiboot
+> |    GRUB    |-------------+
+> +------------+             |
+>       OR                   v
 > +------------+       +-------------+       +--------------+
 > | bootsector |------>| stpdldr.sys |------>| vmstupid.sys |
 > +------------+       +-------------+       +--------------+

kernel/intro.txt

@@ -1,3 +1,5 @@
+File: Introduction
+
 About: kernel memory map
 
 >

kernel/mm/pmm.inc

@@ -0,0 +1,3 @@
+struc
+{
+}