Chore: write changelog for v1.0.0-alpha.4

Author: mxmason

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 Prior to v1.0.0-alpha.1, logs were generated by [`auto-changelog`](https://github.com/CookPete/auto-changelog).
 
+## [v1.0.0-alpha.4](https://github.com/netlify-labs/netlify-plugin-a11y/compare/v1.0.0-alpha.3...v1.0.0-alpha.4)
+### Changed
+- Eliminated some redundancy when defining `directoryFilter` internally.
+- Added a pre-release notice to the README, as well as other copy cleanup.
+
 ## [v1.0.0-alpha.3](https://github.com/netlify-labs/netlify-plugin-a11y/compare/v1.0.0-alpha.2...v1.0.0-alpha.3)
 ### Changed
 - Fixed colors of report printed when using `failWithIssues=true`.