Update changelog

docs/changelog.md

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 # Changelog
 
+## Version 1.4.0
+
+### Added
+
+* Implement directory tree uploads. You can now pass directory paths anywhere you could previously just pass file paths, including the CLI and the Python API. However, note that currently the directory hierarchy won't be preserved. So if you upload `dir_a/file_a.txt` and `dir_b/file_b.txt`, they will simply be downloaded as `file_a.txt` and `file_b.txt` with their directories stripped out. This is a limitation of the current API. See https://github.com/filesender/filesender/issues/1555 for context.
+
 ## Version 1.3.0
 
 ### Changed