Document amd64 platform-specific code

kernel/amd64/bootmain.c

@@ -1,3 +1,5 @@
+/** @file */
+
 #include <amd64/apic.h>
 #include <amd64/debug.h>
 #include <amd64/hpet.h>
@@ -19,8 +21,15 @@
 
 #define UACPI_MEMORY_BUFFER_MAX 4096
 
+/** @cond DOXYGEN_IGNORE */
 ALIGNED (16) static uint8_t uacpi_memory_buffer[UACPI_MEMORY_BUFFER_MAX];
+/** @endcond */
 
+/**
+ * @brief The kernel starts booting here. This is the entry point after
+ * Limine hands control. We set up all the necessary platform-dependent
+ * subsystems/drivers and jump into the init app.
+ */
 void bootmain (void) {
   struct cpu* bsp_cpu = cpu_make ();
   cpu_assign (bsp_cpu->id);