Chore: Add retroactive changelog for v1.0.0-alpha.1

Author: mxmason

CHANGELOG.md

@@ -9,9 +9,15 @@ Generated by [`auto-changelog`](https://github.com/CookPete/auto-changelog).
 
 ## [v1.0.0-alpha.1](https://github.com/netlify-labs/netlify-plugin-a11y/compare/v1.0.0...v1.0.0-alpha.1)
 
-## [v1.0.0](https://github.com/netlify-labs/netlify-plugin-a11y/compare/v1.0.0-beta.1...v1.0.0) - 2021-11-09
+### Changed
+- `resultMode` is now `failWithIssues`, a boolean defaulting to true
+- aXe is now the plugin's default runner
 
-## [v1.0.0-beta.1](https://github.com/netlify-labs/netlify-plugin-a11y/compare/v0.0.12...v1.0.0-beta.1) - 2021-11-09
+### Removed
+- HTML CodeSniffer is no longer supported
+
+### Security
+- Dependencies have been updated.
 
 ### Merged