feat(ctb): Add missing natspec to LivenessGuard and LivenessModule

packages/contracts-bedrock/src/Safe/LivenessGuard.sol

@@ -20,11 +20,20 @@ contract LivenessGuard is ISemver, GetSigners, BaseGuard {
     /// @custom:semver 1.0.0
     string public constant version = "1.0.0";
 
+    /// @notice The safe account for which this contract will be the guard.
     Safe public immutable safe;
 
+    /// @notice A mapping of the timestamp at which an owner last participated in signing a
+    ///         an executed transaction.
     mapping(address => uint256) public lastLive;
+
+    /// @notice An enumerable set of addresses used to store the list of owners before execution,
+    ///         and then to update the lastSigned mapping according to changes in the set observed
+    ///         after execution.
     EnumerableSet.AddressSet private ownersBefore;
 
+    /// @notice Constructor.
+    /// @param _safe The safe account for which this contract will be the guard.
     constructor(Safe _safe) {
         safe = _safe;
     }

packages/contracts-bedrock/src/Safe/LivenessModule.sol

@@ -11,8 +11,11 @@ import { ISemver } from "src/universal/ISemver.sol";
 import { console2 as console } from "forge-std/console2.sol";
 
 /// @title LivenessModule
-/// @notice This module is intended to be used in conjunction with the LivenessGuard. It should be able to
-///         execute a transaction on the Safe in only a small number of cases.
+/// @notice This module is intended to be used in conjunction with the LivenessGuard. In the event
+///         that an owner of the safe is not recorded by the guard during the liveness interval,
+///         the owner will be considered inactive and will be removed from the list of owners.
+///         If the number of owners falls below the minimum number of owners, the ownership of the
+///         safe will be transferred to the fallback owner.
 contract LivenessModule is ISemver {
     /// @notice The Safe contract instance
     Safe public safe;