Changelog updates since v4.0.0 (#14)

Author: milesfrain

CHANGELOG.md

@@ -5,12 +5,15 @@ Notable changes to this project are documented in this file. The format is based
 ## [Unreleased]
 
 Breaking changes:
+- Added support for PureScript 0.14 and dropped support for all previous versions (#11)
 
 New features:
 
 Bugfixes:
 
 Other improvements:
+- Migrated CI to GitHub Actions and updated installation instructions to use Spago
+- Added a CHANGELOG.md file and pull request template (#13, #14)
 
 ## [v4.0.0](https://github.com/purescript/purescript-graphs/releases/tag/v4.0.0) - 2018-06-06