Update the AMDC article `Tutorial: Timing & Sensors` to clarify the location of `extern unit8_t` declaration

Context

Related Issues / PRs:

• https://github.com/Severson-Group/docs.amdc.dev/pull/112
• https://github.com/Severson-Group/docs.amdc.dev/pull/114
• https://github.com/Severson-Group/docs.amdc.dev/pull/123
• https://github.com/Severson-Group/docs.amdc.dev/pull/136

While @hess0297 was doing the AMDC tutorial : Create a GitHub PR that implements tutorial 6 (Timing & Sensors), we encountered the build error (type not found error) in the SDK when declaring:

extern uint8_t sensor_flag;

only if we define this on the "top" of the task_controller.h file as instructed. After some investigation, it looks like we need to define extern uint8_t sensor_flag; after #include "sys/scheduler.h in the task_controller.h, i.e., the following code works:

#ifndef TASK_CONTROLLER_H
#define TASK_CONTROLLER_H

#include "sys/scheduler.h"
#include "drv/analog.h"

extern uint8_t sensor_flag;

but the following does not work:

extern uint8_t sensor_flag;

#ifndef TASK_CONTROLLER_H
#define TASK_CONTROLLER_H

#include "sys/scheduler.h"
#include "drv/analog.h"

Looks like the extern uint8_t sensor_flag; requires to include <stdint.h>, which is actually defined in

https://github.com/Severson-Group/AMDC-Firmware/blob/6eea3d6e4e5d0a44852ddd3233975ac0039c65a8/sdk/app_cpu1/common/sys/scheduler.h#L5

and therefore, extern uint8_t sensor_flag; needed to be located after the #include "sys/scheduler.h".

Approach

Update Tutorial: Timing & Sensors article to clearly specify the location that users should put, especially this section:

Open the linked Tutorial: Timing & Sensors article and find the “Reporting Sensor Acquisition Time and Sensor Data Staleness” section. Clarify where the extern uint8_t sensor_flag declaration belongs relative to the sys/scheduler.h include, then verify the rendered tutorial makes the required placement unambiguous.