Add welcome information when ssh connection

e.g
```
Using username "root".
Authenticating with public key "imported-openssh-key"
Last login: Mon Feb  8 10:33:57 2021 from 129.226.162.133

Welcome to Alibaba Cloud Elastic Compute Service !

You are using the gitlab image powered by Websoft9
docs: https://support.websoft9.com/docs/gitlab

```