fix(docs): improve wording for proof of transfer submission in Core Vault documentation

Author: fassko

docs/fassets/6-core-vault.mdx

@@ -111,7 +111,7 @@ The CV effectively acts as an **insurance-backed reserve** that boosts efficienc
 
 2. **Proof of Payment Submitted**
 
-   Anyone (including the agent) submits proof of the transfer to the FAsset system.
+   Anyone (including the agent) submits the proof of the transfer to the FAsset system.
 
 3. **Verification and Redemption**