added changelog file

CHANGELOG.md

@@ -0,0 +1,23 @@
+# Changes
+
+## 1.2 / 2018-06-05
+
+* Make datadog.checks optional, see [#22][].
+
+## 1.1 / 2018-03-05
+
+* Trust the new GPG key in the APT repository, see [#20][].
+
+## 1.0 / 2018-02-20
+
+* Refactor the formula using a map.
+* Added a Docker compose file to ease development.
+* Added uninstall state.
+* Watch config file for changes, see [#17][].
+* Configure checks, see [#18][].
+
+<!--- The following link definition list is generated by PimpMyChangelog --->
+[#17]: https://github.com/DataDog/datadog-formula/issues/17
+[#18]: https://github.com/DataDog/datadog-formula/issues/18
+[#20]: https://github.com/DataDog/datadog-formula/issues/20
+[#22]: https://github.com/DataDog/datadog-formula/issues/22