cli: [FIX] Fix target add command (not store targets at config file)

[mdjunior]

This PR fixes an incorrect behavior at target-add command.

Running target-add command before, new target is not add to config file:

$ gsh target-add example https://gsh-api.example.org -s
Using config file: /Users/manoel.junior/.gsh/config.yaml

$ cat /Users/manoel.junior/.gsh/config.yaml
{}

This error happen because viper.Set() is not invoked to save targets at config file. Is a simple commit (1 line) 1202cd4.

Other points is that target-* commands don't have a result message to user. Example:

$ gsh target-add example https://gsh-api.example.org -s
Using config file: /Users/manoel.junior/.gsh/config.yaml

This PR addresses it, adding messages explaining to user what is happen after running command with success state (wiki page updated).

Finally, this PR changes name of GSH CLI from gshc to gsh at code and wiki. Homebrew and snap installs GSH CLI as gsh command and at this way is more clear to user this name.

[rafaveira3]

Good catch, @mdjunior ! Sounds good to me.