Add Attributes code to the 'Annotation Routes' section

[BahmanMD]

Add Attributes code to the 'Annotation Routes' section and update page_creation.rst

[javiereguiluz]

@BahmanMD thanks for improving this and congrats on your first Symfony Docs contribution 🎉

Please note that while merging this pull request I did some minor tweaks (see 90936ab).

I removed the caution because those are reserved for things like dangerous features or irreversible actions. In the code blocks I replaced tabs by white spaces, because that's the syntax used in Symfony Docs. In any case, all this is minor and all the important things from your pull request remained. Thanks!