Remove the description in the README about rebuilding the image

[xiao-jay]

fix #15 test step：

1、deploy a standard change image from apache/kvrocks:2.3.0 to apache/kvrocks:nightly

kubectl apply -f examples/standard.yaml

2、exec redis-cli in pod

➜  kvrocks-operator git:(unstable) ✗ kubectl exec -it kvrocks-standard-1-demo-0 -n kvrocks -- /bin/bash
root@kvrocks-standard-1-demo-0:/kvrocks# redis-cli
127.0.0.1:6379> 

other error fix: image bitnami/kube-rbac-proxy:0.14.0 not have tag v0.14.0

[ColinChamber]

This project was donated to the kvrocks-community by Boss-Zhipin. Although it has been running smoothly in their production, the community version is not user-friendly enough. Thank you for helping to fix it. @xiao-jay