Update isp-netflow-surveillance-and-vpn.md

[JoshuaBlinkhorn]

Minor fixes for grammar and typographical errors.

PR type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update
• Refactoring (no functional changes, no api changes)
• Build related changes
• [x ] Documentation content changes
• Other... Please describe:

PR checklist

Please check if your PR fulfills the following requirements:

• [ x] I have read the CONTRIBUTING.md doc
• [ x] The Git workflow follows our guidelines: CONTRIBUTING.md#git
• [ N/A] I have added necessary documentation (if appropriate)

What is the current behavior?

Issue number: N/A

What is the new behavior?

Minor changes to wording in documentation.

Does this PR introduce a breaking change?

• Yes
• [ x] No

Other information

[JoshuaBlinkhorn]

Are we using squash and merge? This would allow us to name the commit according to the rules in CONTRIBUTING.md.

If not, I’ll close this PR and raise another with the commit named properly.