[release notes] Write release notes for the 2.3.0 - the main change i…

…s the Python version.

release_notes/2.3.0.md

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+## New features:
+
+* \#282, \#316 Updating Python to Python 3.12. If on a Mac or on Linux, you need to update your Mac Python to 3.12, on Windows Python is shipped together with the Orm.
+* No longer supporting Windows 7, as there is no Python 3.12 for it. Windows 7 was EOL January 2020.
+* \#309 The About Dialog now shows the version
+
+## Synths:
+
+* Kawai K4: Added adaptation to the release bundle, was missing from it (\#313)
+
+## Bug fixes:
+
+* \#310 Paging buttons were not renumbered when the count of pages changed due to tagging  
+* \#316 Fix crash on exit on Mac when no Python was installed
+* Mac builds now use the keg-only distribution of ICU4C installed via homebrew, using brew --prefix to determine where it is