Add Staking Introduction and Proxy Account Guide

[thomivy]

Summary of changes

Adds:

• Comprehensive Staking intro under Use

  

• Proxy Account Add/Remove guide under Use

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Code Checklist

• [x] I have tested that prove my changes are working as intended
• [x] I have added necessary documentation (if appropriate)

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[thomivy]

The deploy preview is not rendering it correctly, probably cache again, though I re-triggered it. Locally the pages show fine, no issues.