Update Serving_Configure_EN.md

doc/Serving_Configure_EN.md

@@ -389,8 +389,13 @@ op:
             #use_mkldnn
             #use_mkldnn: True
 
-            #ir_optim
+            #ir_optim, When running on TensorRT，must set ir_optim=True
             ir_optim: True
+            
+            #precsion, Decrease accuracy can increase speed
+            #GPU 支持: "fp32"(default), "fp16", "int8"；
+            #CPU 支持: "fp32"(default), "fp16", "bf16"(mkldnn); 不支持: "int8"
+            precision: "fp32"
     rec:
         #concurrency，is_thread_op=True，thread otherwise process
         concurrency: 3