docs(vpn): add a blank line before the first-level heading in the VPN user document

[profoundwu]

What this PR does / why we need it: add a blank line before the first-level heading in the VPN user document Which issue this PR fixes: (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged) fixes #xxx

Special notes for your reviewer:

Release note:

1.  add a blank line before the first-level heading in the VPN user document

PR Checklist

• [ ] Tests added/passed.

• [x] Documentation updated.

• [ ] Schema updated.

• [ ] CheckDeleted.

  • a. During query operation (Read Context) aa. Resource not found >>>>>> Paste the screenshot here <<<<<<

  • b. During delete/disassociate/unbind operation (Delete Context) ba. Resource not found >>>>>> Paste the screenshot here <<<<<<