Update the news of upgrading mainnet to v0.7.2

Author: zjshen14

README.md

@@ -2,6 +2,7 @@
 
 ## News
 
+- Please upgrade MainNet to v0.7.2. Delegates only need to restart the node with the docker image tagged `v0.7.2`.
 - TestNet is upgraded to v0.7.2. (2019-07-11)
 - TestNet is upgraded to v0.7.1 with a fix in API to sort actions on one address correctly. (2019-07-02)
 - TestNet is upgraded to v0.7.0. If you join the previous TestNet, you DO NOT need to clean up your local database.
@@ -20,18 +21,18 @@ You only need to load the up-to-date genesis file again (`curl https://raw.githu
 
 Here are the software versions we use:
 
-- MainNet: [v0.6.2](https://github.com/iotexproject/iotex-core/tree/2df78e9460dee3bd3d96526468472409ac36d615)
+- MainNet: [v0.7.2](https://github.com/iotexproject/iotex-core/tree/909a087ce8a3aa1ae53e3f918f18d097226e11d2)
 - TestNet: v0.7.2
 
 ## <a name="mainnet"/>Join MainNet Alpha
 
 1. Pull the docker image:
 
 ```
-docker pull iotex/iotex-core:v0.6.2
+docker pull iotex/iotex-core:v0.7.2
 ```
 
-Please check if the docker image digest is `d710efc6c76ad7e79414ef26e6386771de091767bd078eb9f7f32c79b3087692`.
+Please check if the docker image digest is `0ed123a65c24188e1c2497574d885658dce2b8977b5caed6031c9673055fd4d3`.
 
 2. Set the environment with the following commands:
 
@@ -70,7 +71,7 @@ docker run -d --restart on-failure --name iotex \
         -v=$IOTEX_HOME/log:/var/log:rw \
         -v=$IOTEX_HOME/etc/config.yaml:/etc/iotex/config_override.yaml:ro \
         -v=$IOTEX_HOME/etc/genesis.yaml:/etc/iotex/genesis.yaml:ro \
-        iotex/iotex-core:v0.6.2 \
+        iotex/iotex-core:v0.7.2 \
         iotex-server \
         -config-path=/etc/iotex/config_override.yaml \
         -genesis-path=/etc/iotex/genesis.yaml
@@ -89,7 +90,7 @@ docker run -d --restart on-failure --name iotex \
         -v=$IOTEX_HOME/log:/var/log:rw \
         -v=$IOTEX_HOME/etc/config.yaml:/etc/iotex/config_override.yaml:ro \
         -v=$IOTEX_HOME/etc/genesis.yaml:/etc/iotex/genesis.yaml:ro \
-        iotex/iotex-core:v0.6.2 \
+        iotex/iotex-core:v0.7.2 \
         iotex-server \
         -config-path=/etc/iotex/config_override.yaml \
         -genesis-path=/etc/iotex/genesis.yaml \