Update emulators.md

[starimploie]

Added emulator startup information and clarified the environment.useEmulators. Updated the localhost address

Checklist

• Issue number for this PR: Update emulators.md #3308 (required)
• Docs included?: yes
• Test units included?: not required. doc change only
• In a clean directory, yarn install, yarn test run successfully? doc change only

Description

Code sample

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[starimploie]

signed cla

[davideast]

@starimploie Thank you!!!