add doc

velox/type/Timestamp.h

@@ -187,7 +187,7 @@ struct Timestamp {
   /// Due to the limit of std::chrono, throws if timestamp is outside of
   /// [-32767-01-01, 32767-12-31] range.
   /// If allowOverflow is true, integer overflow is allowed in converting
-  /// timestmap to milliseconds.
+  /// timestamp to milliseconds.
   std::chrono::time_point<std::chrono::system_clock, std::chrono::milliseconds>
   toTimePoint(bool allowOverflow = false) const;
 
@@ -313,6 +313,8 @@ struct Timestamp {
 
   // Assuming the timestamp represents a GMT time, converts it to the time at
   // the same moment at zone.
+  // If allowOverflow is true, integer overflow is allowed in converting
+  // timestamp to TimePoint, otherwise we throw.
   // Example: Timestamp ts{0, 0};
   // ts.Timezone("America/Los_Angeles");
   // ts.toString() returns December 31, 1969 16:00:00