docs: add a changelog

Author: alexktzk

CHANGELOG.md

@@ -0,0 +1,9 @@
+## 1.0.0 (2019-02-17)
+
+### Added
+
+* Ability to edit single card settings ([c227095](https://github.com/trello/glitch-trello-power-up/commit/c227095))
+* Ability to specify default difficulty for a task ([5576e20](https://github.com/trello/glitch-trello-power-up/commit/5576e20))
+* Ability to sync only the cards that was assigned to user ([ff83100](https://github.com/trello/glitch-trello-power-up/commit/ff83100))
+* Simple auth system ([88f2c29](https://github.com/trello/glitch-trello-power-up/commit/88f2c29))
+* Store user id and api token in the local storage ([5a7ae1d](https://github.com/trello/glitch-trello-power-up/commit/5a7ae1d))