[Bug]: should mention install IL2CPP in doc

[harleyzhd]

JEngine Version

1.1.5

Unity Version

6000.3

Target Platform

Windows

Bug Description

Steps to Reproduce

Build All

Expected Behavior

Successfully built package

Error Logs

Additional Context

No response

Checklist

• I have searched existing issues to ensure this bug hasn't been reported before
• I have tested with the latest version of JEngine

[JasonXuDeveloper]

mentioned in https://jengine.xgamedev.net/en/docs/v1.0/faq#packaging-and-publishing