Add release notes

RELEASE_NOTES.md

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+This is a minor bug fix release. We fixed problems that were detected by static
+code analysis tools and we did a couple of other minor fixes. Apart from that
+there has been improved logging/debugging to file. We slightly changed the log
+format to make logs more readable. At the end we introduced changes to automate
+code analysing and releasing process. We hope it will help in providing new releases
+more frequent.
+
+Changes:
+ - Use new logging interface
+ - Update Polish translations
+ - Update dependencies in composer.json
+ - Fix remove directive button for storage directives
+ - Fix qrcodejs version in composer.json
+ - Fix problem found in static code analysis
+ - Hide reset to default value button for storage directives
+ - Improve coding style according to PSR-12
+ - Update flotr2 include path
+ - Update LICENSE file