Update set-up-app-links.md (add missing line)

[Reza-Babakhani]

<meta-data android:name="flutter_deeplinking_enabled" android:value="true" />

This one line of code took me 3 days.
Without this, deep linking doesn't work.

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[parlough]

Thanks for the PR to fix this and sorry about the confusion you met. I'll defer to others to review:

@chunhtai or @hannah-hyj would you mind taking a look at this PR? Thank you!

[hannah-hyj]

@Reza-Babakhani Sorry for the confusion you encountered and thank you for filing this.

Starting from Flutter version 3.27 ( the latest stable) , the deep link flag is set to true by default, so this line is no longer needed.
However, for Flutter versions earlier than 3.27, this line is still necessary.

I think we should add back this line, but include it as a note:
"If you are using a Flutter version earlier than 3.27, add the following metadata tag:
<meta-data android:name="flutter_deeplinking_enabled" android:value="true" />

the iOS setup guide should be updated as well, same situation with the flag for iOS. I can do that in a separate PR.

Thank you for reminding us of this. The latest stable version was just launched, and most users are still on earlier versions, so adding back this line to the guide is essential.