Add extra newline after additionalHelp output

The additionalHelp message is printed at the end of the --help output;

    To get more help with docker, check out our guides at https://docs.docker.com/go/guides/
    PS>

As this message may contain an URL, users may copy/paste the URL to open it
in their browser, but can easily end up copying their prompt (as there's
no whitespace after it), and as a result end up on a broken URL, for example:

    https://docs.docker.com/go/guides/PS

This patch adds an extra newline at the end to provide some whitespace
around the message, making it less error-prone to copy the URL;

    To get more help with docker, check out our guides at https://docs.docker.com/go/guides/

    PS>

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Author: thaJeztah

cli/cobra.go

@@ -511,6 +511,7 @@ Run '{{.CommandPath}} COMMAND --help' for more information on a command.
 {{- if hasAdditionalHelp .}}
 
 {{ additionalHelp . }}
+
 {{- end}}
 `