Update keyboard.h

fixing missing includes and definition

kernel/keyboard.h

@@ -1,7 +1,10 @@
 #ifndef KEYBOARD_H
 #define KEYBOARD_H
 
+#include <stint.h>
+
 void keyboard_init(void);
+void keyboard_buffer_add(char c);
 char keyboard_get_char(void);  // Blocking read from buffer
 extern const char scancode_map[128];