docs: Update USAGE.md to prevent query double encoding

[SGudbrandsson]

The documentation recommends urlencoding data when checking message activity.

This causes a double encoding problem.

Fixes

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the development branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

• Updates documentation to prevent double encoding of queries

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[SendGridDX]

All committers have signed the CLA.

[thinkingserious]

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