Update ReadMe.md

Add new text in line 181.

Author: SamFu1113

ReadMe.md

@@ -178,4 +178,4 @@ If I use other commands other than P() and V(), I will get 0 points.
     The initial values of semaphores are very important. Semaphore values must be greater than 0. There are no points in setting a negative semaphore value. Before and after the *printf* statements, please use ```P()```, ```V()``` to achieve your goal. Good luck.  
     In ```sem.c```, the following two functions are provided for me to observe and debug. I cannot use them in the final program. If I use, 0 point will be graded.  
     ```get_blocked_no(semid)```: return the number of processes  
-    ```get_sem_val(semid)```:
+    ```get_sem_val(semid)```: return the semaphore value of semid.