Improve the jcli completion document

[LinuxSuRen]

inspire from kubectl

Make sure that you've checked the boxes below before you submit PR:

Always

• Make sure you are requesting to pull a topic/feature/bugfix branch (right side) and not your master branch!
• Written well with PR title, we generate the release notes base on that

For the bug fixes or features only

• Quality Gate Passed. Change this URL to your PR.
• The coverage is xxx on the new lines
• I've tested it by manual in the following platform
  • MacOS
  • Linux
  • Windows