doc: introduce a CHANGELOG.md file

[skip ci]

Author: flavorjones

CHANGELOG.md

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+# rails-dom-testing changelog
+
+## next / unreleased
+
+### Added
+
+* Introduce test helpers `assert_not_dom`, `assert_not_select`, and the "refute" equivalents. #113 @joshuay03
+
+
+### Improved
+
+* `assert_select` now raises an error when given an invalid Range or invalid combination of `:minimum` and `:maximum`. #115 @joshuay03
+* `assert_select` now raises an error when given a block with a 0 element assertion. #116 @joshuay03
+
+
+### New Contributors
+
+* @joshuay03 made their first three contributions in this release.
+
+
+## v2.2.0 / 2023-08-03
+
+### What's Changed
+
+* Allow user to choose the HTML parser used by @flavorjones in https://github.com/rails/rails-dom-testing/pull/109
+* Fix string substitution regression by @nicoco007 in https://github.com/rails/rails-dom-testing/pull/110
+
+### New Contributors
+
+* @nicoco007 made their first contribution in https://github.com/rails/rails-dom-testing/pull/110