[DOC]  NEP-621: Tokenized Vault

### Documentation Type

New Documentation

### What needs documentation?

https://github.com/near/NEPs/pull/621/files?short_path=f87427d#diff-f87427d70b829a6b74892c568d1bf2fc032bee80b219c0971216e0550c26cae3

### Acceptance Criteria

-

### Resources & References

_No response_

### Priority

🔴 P0 : Missing Critical Documentation