Update participant-agreement.md

[kmori]

Updating the language in the participant agreement to match our current Google Doc template language for research with compensation and without compensation.

For more context on how/why these updates were made- @jstrothman & @kmori made edits to the participant agreement with the goals to:

• Increase plain language
• Reduce power imbalance of language in previous consent form
• Explain how information will be used
• Ask for consent on a more granular basis & explain opportunities to change your mind about consent
• Create a working document for more frequent iteration

We also went through a review process with OGC, Privacy, and the TTS Research Guild:

• 7/26/2022: OGC reviewed and approved updated language
• 7/26/2022: CPO confirmed it’s acceptable to link to the Privacy Act statement rather than include in full.
• 8/05/2022: Reviewed the new consent form with the Research Guild and made changes based on comments and feedback
• 9/20/2022: OGC provided guidance that the agreements would need to be signed with either a wet signature or GSA’s DSS (DocuSign)

These changes were initially made in our internal Google Docs and this pull request is to publish those changes in a publicly accessible setting.