Should update the CHANGELOG.md after release #574
Description
Document that step in the manual release steps so that we remember to do it. Pointed out on https://github.com/impress/impress.js/pull/572/files#r69710339
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Document that step in the manual release steps so that we remember to do it. Pointed out on https://github.com/impress/impress.js/pull/572/files#r69710339