docs: fix formatting

Author: john-light

docs/index.md

@@ -17,7 +17,8 @@ with features such as:
 - **Vaults**, "transfers must wait `N` days after being initiated to be effectuated,
   and can be cancelled in the mean time"
 
-- **Subscriptions**, "address `0x123...9a` can withdraw up to `v` BTC per month from this account"
+- **Subscriptions**, "address `0x123...9a` can withdraw up to `v` BTC 
+per month from this account"
 
 - **Strong privacy**, "transaction details are end-to-end encrypted
   and verified using a zero-knowledge proof"