Add release instructions (#20)

Author: MartinHjelmare

RELEASE.md

@@ -0,0 +1,8 @@
+# Release procedure
+
+- Create a release branch from master.
+- Update version in `VERSION`to the new version number, eg `'0.2.0'`.
+- Commit with commit message `Bump version to 0.2.0` and push the release branch to origin.
+- Create a pull request from release branch to `master` with the upcoming release number as the title.
+- Squash merge the pull request into `master`.
+- Go to GitHub releases page and publish the current draft release, setting the correct title and tag version from master branch.