docs: use "keep a changelog" format (#279)

Author: nozaq

CHANGELOG.md

@@ -1,10 +1,13 @@
-### [1.0.1](https://github.com/nozaq/terraform-aws-secure-baseline/compare/v1.0.0...v1.0.1) (2022-03-06)
+# Changelog
+All notable changes to this project will be documented in this file.
 
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.0.1](https://github.com/nozaq/terraform-aws-secure-baseline/compare/v1.0.0...v1.0.1) (2022-03-06)
 ### Bug Fixes
-
-* avoid for_each key error ([#273](https://github.com/nozaq/terraform-aws-secure-baseline/issues/273)) ([0122d6f](https://github.com/nozaq/terraform-aws-secure-baseline/commit/0122d6fcd00ecd1114a2d5e7853027ebb0322d71))
-* mark `var.member_accounts` required ([#272](https://github.com/nozaq/terraform-aws-secure-baseline/issues/272)) ([8612941](https://github.com/nozaq/terraform-aws-secure-baseline/commit/8612941317db8c5f3eb82fd8c5218b8ef5a5d41f))
+- avoid for_each key error ([#273](https://github.com/nozaq/terraform-aws-secure-baseline/issues/273)) ([0122d6f](https://github.com/nozaq/terraform-aws-secure-baseline/commit/0122d6fcd00ecd1114a2d5e7853027ebb0322d71))
+- mark `var.member_accounts` required ([#272](https://github.com/nozaq/terraform-aws-secure-baseline/issues/272)) ([8612941](https://github.com/nozaq/terraform-aws-secure-baseline/commit/8612941317db8c5f3eb82fd8c5218b8ef5a5d41f))
 
 ## [1.0.0] - 2022-02-19
 ### Feat
@@ -419,7 +422,6 @@ after upgrade. See `docs/upgrade-1.0.md` for guidance.
 <a name="0.0.1"></a>
 ## 0.0.1 - 2018-02-12
 
-[Unreleased]: https://github.com/nozaq/terraform-aws-secure-baseline/compare/1.0.0...HEAD
 [1.0.0]: https://github.com/nozaq/terraform-aws-secure-baseline/compare/0.34.0...1.0.0
 [0.34.0]: https://github.com/nozaq/terraform-aws-secure-baseline/compare/0.33.0...0.34.0
 [0.33.0]: https://github.com/nozaq/terraform-aws-secure-baseline/compare/0.32.0...0.33.0