Prepare changelog for next release

Author: ashwinvis

CHANGELOG.md

@@ -1,3 +1,12 @@
+# 0.2.0 (2021-06-16)
+
+* Optional support for Mermaid.js diagrams
+- Fine grained tests using pytest and Selenium which validate the content
+- CI moved to Github Actions
+- Upgrade highlight.js and socket.io versions
+- Verbose log messages
+- Contributions now welcome at [Open Collective](https://opencollective.com/instant-markdown)!
+
 # 0.2.0.rc2 (2019-10-15)
 
 * Bug fix: PUT request and response for node>10