Update protect-hybrid-cloud-networks-with-cloudflare-magic-transit.mdx

[Vincent-cf]

Adding comment to reinforce use case 1 requires Cloud BYOIP to work

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Documentation checklist

• The documentation style guide has been adhered to.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.
• Files which have changed name or location have been allocated redirects.

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