Add a detailed documentation link to the nnictl command in the command prompt.

[rabbit008]

At present, after the user submits the NNI task, he will see a brief description of the nnictl * command, but most of the commands are not unique and cannot be detailed due to the limitation of the location. I hope that the address of the detailed document can be added to the page for the user to view.

What would you like to be added: The address of the detailed document

Why is this needed:User-friendly

Without this feature, how does current nni work：Users need to go to the web page to find the corresponding instructions themselves.

Components that may involve changes:As above

Brief description of your proposal if any:As above,may be like this: