update CHANGELOG following v0.1.0 release

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5830749..975714f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,5 @@
+# 0.2.0 (Unreleased)
+
 # 0.1.0 (July 3, 2020)
 
 Initial release.