Adding hint for skip SSL validation option.

[a2geek]

--skip-ssl-validation did not show an env variable hint; went to add it; found that BLACKSMITH_SKIP_VERIFY already existed; realized it just wasn't shown as an option at the CLI; showing in help.

With update:

  -k, --skip-ssl-validation
                  Skip verification of the API endpoint
                  Defaults to $BLACKSMITH_SKIP_VERIFY

[norman-abramovitz]

LGTM