[Pages] fix incorrect instructions for managing multiple environments

[10p-freddo]

Fixes #1820

[gmemstr]

@deadlypants1973 Any news on getting this reviewed/merged? I imagine this is a stumbling block for quite a few people exploring Cloudflare Pages for use (myself included)!

[gitguardian[bot]]

⚠️ GitGuardian has uncovered 4 secrets following the scan of your pull request.

Please consider investigating the findings and remediating the incidents. Failure to do so may lead to compromising the associated services or software components.

🔎 Detected hardcoded secrets in your pull request

GitGuardian id	Secret	Commit	Filename
-	Generic High Entropy Secret	7d3d958ba7e1005d201a7e62289737fd5d716394	config.toml	View secret
-	Generic High Entropy Secret	58b6333afd7670da52bd237bec6b2c0cb708ae5e	products/ddos-protection/docs-config.js	View secret
-	Generic High Entropy Secret	f5ad72dcb5f9b6b4072be76c18ee663e52f30f72	products/ddos-protection/docs-config.js	View secret
3543783	Generic High Entropy Secret	51cbbada456648d933bd539e901cb20bb22d0adb	products/ruleset-engine/docs-config.js	View secret

🛠 Guidelines to remediate hardcoded secrets

1. Understand the implications of revoking this secret by investigating where it is used in your code.
2. Replace and store your secrets safely. Learn here the best practices.
3. Revoke and rotate these secrets.
4. If possible, rewrite git history. Rewriting git history is not a trivial act. You might completely break other contributing developers' workflow and you risk accidentally deleting legitimate data.

To avoid such incidents in the future consider

• following these best practices for managing and storing secrets including API keys and other credentials
• install secret detection on pre-commit to catch secret before it leaves your machine and ease remediation.

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<sup>🦉 GitGuardian detects secrets in your source code to help developers and security teams secure the modern development process. You are seeing this because you or someone else with access to this repository has authorized GitGuardian to scan your pull request.

Our GitHub checks need improvements? Share your feedbacks!</sup>