update changelog

CHANGELOG.md

@@ -21,6 +21,7 @@ All notable changes to this project will be documented in this file.
 - `utils.uvcalibrate` will error rather than warn if some of the newly added checks do not pass, including if antenna names do not match between the objects, starting in version 2.2. In addition, the `flag_missing` keyword is deprecated and will be removed in version 2.2.
 
 ### Fixed
+- UVFlag.__add__ now properly concatenates all existing data-like parameters of the object, including optional ones.
 - A bug in `UVData.downsample_in_time` where the data were not being properly weighted by the nsample array and the nsample_array was not being properly weighted by the integration times.
 - A bug in `UVData.downsample_in_time` that lead to duplicated data on the final object if a baseline had varying integration times and some integration times were greater than or equal to the requested minimum integration time.