docs: add message about the freezing for the audit

[chechu]

Description

Resolves #

Checklist

• I have updated the documentation to account for the changes in the code.
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a test preventing this bug from silently reappearing again.
• My contribution follows Venus contribution guidelines.

[github-actions]

Package	Line Rate	Branch Rate	Health
Comptroller	100%	90%	✔
Comptroller.Diamond	95%	59%	✔
Comptroller.Diamond.facets	73%	62%	➖
Comptroller.Diamond.interfaces	100%	100%	✔
DelegateBorrowers	100%	86%	✔
Governance	26%	25%	❌
InterestRateModels	0%	0%	❌
Lens	41%	37%	❌
Liquidator	99%	89%	✔
Oracle	100%	100%	✔
PegStability	88%	84%	✔
Swap	88%	58%	✔
Swap.interfaces	100%	100%	✔
Swap.lib	81%	55%	✔
Tokens	100%	100%	✔
Tokens.VAI	71%	46%	➖
Tokens.VRT	20%	9%	❌
Tokens.VTokens	35%	20%	❌
Tokens.XVS	19%	8%	❌
Utils	53%	35%	➖
VRTVault	49%	36%	❌
Vault	50%	45%	➖
XVSVault	65%	52%	➖
Summary	55% (2234 / 4054)	40% (927 / 2304)	➖