Update README.md

Author: Choi TaeHo

README.md

@@ -1,38 +1,46 @@
 <p align="center"><img width="40%" src="./img/pytorch.png"></p>
 
-## Multi Machine Tutorial for Pytorch
-xxxxx
+# Multi Machine Tutorial for Pytorch
+It works TCP communication for multi-gpu processing.
+They automatically find unused port address and 
 
 ## Requirements
 * pytorch : 1.5
 * CUDA : 10.1
 
-## Base
-
-### Single Machine
+## Multi GPU in Single Machine
+For only multi-gpu processing in single machine, you only need to clarify `num-gpu` argument.
 ```bash
 CUDA_VISIBLE_DEVICES='0,1' python -m src.tools.check_dist --num-gpu 2
 ```
 
+
+## Multi Machines
+### Main Machine
+[For collective communication](https://tutorials.pytorch.kr/intermediate/dist_tuto.html#collective-communication) in pytorch, it needs to execute process in main machine.
+They automatically set main machine ip address and unused port number for TCP communication.
+`num-machine`
+set `machine-rank` to zero.
 ```bash
-CUDA_VISIBLE_DEVICES='0,1' python -m src.tools.check_dist --num-gpu 2 --dist_port 47515
+CUDA_VISIBLE_DEVICES='0,1' python -m src.tools.check_dist --num-gpu 2 --num-machine 2 --machine-rank 0
 ```
 
-### Multi Machines
-* Main Machine
-
+When you want to use a fixed port number, just clarify `dist-port` argument.
 ```bash
-CUDA_VISIBLE_DEVICES='0,1' python -m src.tools.check_dist --num-gpu 2 --num-machine 2 --machine-rank 0
+CUDA_VISIBLE_DEVICES='0,1' python -m src.tools.check_dist --num-gpu 2 --num-machine 2 --machine-rank 0 --dist-port xxxxx
 ```
 
-* Other Machines
+### Other Machines
+In other machines, you clarify `machine-rank` within the range of 1~(num_machine-1).
+And you must set `dist-ip` and `dist-port` arguments which is the same with main machine values.
 
 ```bash
-CUDA_VISIBLE_DEVICES='0,1' python -m src.tools.check_dist --num-gpu 2 --num-machine 2 --machine-rank 1 --dist_ip xxx.xxx.xxx.xxx --dist_port xxxxx
+CUDA_VISIBLE_DEVICES='0,1' python -m src.tools.check_dist --num-gpu 2 --num-machine 2 --machine-rank 1 --dist-ip xxx.xxx.xxx.xxx --dist-port xxxxx
 ```
 
 ## Test
-
+Examples for collective communication functions in single machine.
+It also can be executed in multi-machine settings.
 ### Gather
 ```bash
 CUDA_VISIBLE_DEVICES='0,1' python -m src.tools.gather --num-gpu 2