message: Document that write_concern timeout of zero means no timeout
diff: @@ -140,11 +140,11 @@ class MONGOCXX_API write_concern {
  ///
  /// Requires that a majority of the nodes in a replica set acknowledge a write operation before
  - /// it is considered a success. A timeout is required when setting this write concern.
  + /// it is considered a success.
  ///
  /// @param timeout
  /// The amount of time to wait before the write operation times out if it cannot reach
  - /// the majority of nodes in the replica set.
  + /// the majority of nodes in the replica set. If the value is zero, then no timeout is set.
  ///
  /// @throws mongocxx::logic_error for an invalid timeout value.
  //
  @@ -166,7 +166,8 @@ class MONGOCXX_API write_concern {
  /// concern cannot be satisfied within the timeout, the operation is considered a failure.
  ///
  /// @param timeout
  - /// The timeout (in milliseconds) for this write concern.
  + /// The timeout (in milliseconds) for this write concern. If the value is zero, then no
  + /// timeout is set.
  ///
  /// @throws mongocxx::logic_error for an invalid timeout value.
  ///
  