Fix a few typos in SDK_SPEC

[albertchae]

Description

Fix some typos in SDK_SPEC.md

Also replaced tabs with spaces for Event, since there was a mix of both
which was causing them to misalign. Other code blocks are using tabs
too, but since they are all tabs, they do align correctly.

Also fix indentation on 4.1.3 so step 5 renders properly

Type of change (choose one)

• Chore (refactors, upgrades, etc.)
• Bug fix (non-breaking change that fixes an issue)
• Security fix (non-breaking change that fixes a potential vulnerability)
• Docs
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality not to work as expected)

Checklist

• I've linked any associated issues to this PR.
• I've tested my own changes.

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