Add missing --code-style flag in CLI documentation

[shadforth]

Description

This adds the missing --code-style flag from the command line docs.

Currently, running ktlint generateEditorConfig intellij_idea will generate error:

Error: got unexpected extra argument (intellij_idea)
Error: missing option --code-style

Checklist

Before submitting the PR, please check following (checks which are not relevant may be ignored):

• Commit message are well written. In addition to a short title, the commit message also explain why a change is made.
• At least one commit message contains a reference Closes #<xxx> or Fixes #<xxx> (replace<xxx> with issue number)
• Tests are added
• KtLint format has been applied on source code itself and violations are fixed
• PR title is short and clear (it is used as description in the release changelog)
• PR description added (background information)

[paul-dingemans]

Tnx for fixing!