[docs][utest]:Add comments for smp_thread_preemption

Add comments for smp_thread_preemption.

Signed-off-by: Mengchen Teng <teng_mengchen@163.com>

src/utest/smp/smp_thread_preemption_tc.c

@@ -18,6 +18,28 @@
  *          high-priority threads preempt low-priority threads, and
  *          print the current status of each core in the thread's entry function.
  *
+ * Test Case Name: [smp_thread_preemptions]
+ *
+ * Test Objectives:
+ * - Test the thread preemption logic under the SMP architecture
+ *
+ * Test Scenarios:
+ * - A high-priority thread thigh and a low-priority thread tlow are created. Since tlow is created
+ * - prior to thigh, it prints the thread list information first and then waits for the finish_flag
+ * - bit. Once thigh becomes ready, it preempts tlow, prints the thread list, and then sets the
+ * - finish_flag bit. After that, tlow exits the busy-wait loop.
+ *
+ * Verification Metrics:
+ * - First, the message "Low priority thread is running" will be displayed, followed immediately by
+ * - a thread_list information list. Subsequently, the message "High priority thread is running" will
+ * - appear, and in the thread_list that follows, the tlow thread can be observed in the ready state.
+ *
+ * Dependencies:
+ * - Enable RT_USING_SMP, set RT_THREAD_PRIORITY_MAX = 256.
+ *
+ * Expected Results:
+ * - You will see the message "[ PASSED ] [ result ] testcase (core.smp_thread_preemptions)", and observe
+ * - the tlow thread in the ready state in the thread_list printed by the thigh thread.
  */
 
 #define THREAD_PRIORITY_HIGH 21