chore: Add unreleased section to CHANGELOG to keep track of changes (argoproj-labs#7)

Author: jannfis

CHANGELOG.md

@@ -4,6 +4,22 @@ This is the change log for `argocd-image-updater`. Please read thoroughly
 when you upgrade versions, as there might be non-obvious changes that need
 handling on your side.
 
+## Unreleased
+
+### Upgrade notes (no really, you MUST read this)
+
+### Bug fixes
+
+N/A
+
+### New features
+
+N/A
+
+### Other changes
+
+refactor: Reduced number of necessary ArgoCD API requests (#4)
+
 ## 2020-08-06 - Release v0.1.1
 
 Quick bug-fix release to get rid of some left-over working names