[modify describe arm]

README.md

@@ -45,13 +45,15 @@ mkdir build && cd build
 cmake .. && cmake --build .
 ```
 
-if compiling on an ARM processor(aarch64 or aarch32), you need add one parameter:
+To compile on an ARM processor (aarch64 or aarch32), please add option CPUTYPE as below:
 
-```cmd
 aarch64:
+```cmd
 cmake .. -DCPUTYPE=aarch64 && cmake --build .
+```
 
 aarch32:
+```cmd
 cmake .. -DCPUTYPE=aarch32 && cmake --build .
 ```