Add debug/sandbox mention again

Author: rzats

src/client/packaging/pypi/CHANGELOG.md

@@ -8,6 +8,11 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/).
 ### Includes
 - https://github.com/cmu-delphi/delphi-epidata/pull/1363
 
+### Added
+- Adds two debug flags:
+  - `debug` logs info about HTTP requests and responses
+  - `sandbox` prevents any HTTP requests from actually executing, allowing for tests that do not incur server load.
+
 ### Changed
 - Replaced use of deprecated setuptools' `pkg_resources` library with the native `importlib.metadata` library.