Enhance Documentation to Clarify "Thawing a Signer" Behavior

[ColePBryan]

In light of recent audit feedback, there's a need to provide a clearer explanation in our documentation about the "Thawing a Signer" process and its implications for indexers. By detailing this, we aim to ensure indexers understand how to appropriately respond when a signer is thawed. The updated documentation will emphasize:

• The intent of thawing as an early warning about a signer's impending invalidation.
• The suggested actions for indexers, based on whether they have or haven't engaged with the signer.

This enhancement will provide clarity and guidance for our user community. For a detailed context, refer to #38 .