docs: add a simple CHANGELOG.md that references GH releases (#419)
docs: add a simple CHANGELOG.md that references GH releases (#419)

- we have release notes already in GH releases, so add a simple `CHANGELOG.md` that references it
  - I use something similar in most of my libraries

- this should hopefully make it easier for users to find the release notes in case they hadn't seen them on GH before
ezolenko/rollup-plugin-typescript2,ezolenko/rollup-plugin-typescript2