Update ValidateFormatPlugin Documentation - additional options command

[vincentclee]

I noticed the command to enable additional options for the ValidateFormatPlugin are a bit different than what is described -
https://github.com/manheim/terraform-pipeline/blob/master/docs/ValidateFormatPlugin.md

Here are my recommendations

ValidateFormatPlugin.withRecursive()
                    .withDiff()
                    .init()

change to

TerraformFormatCommand.withRecursive()
                      .withDiff()
ValidateFormatPlugin.init()

Also, a few spelling points:

• Additonal to Additional
• recusively to recursively

🇺🇸