Added polish guide
Merge branch 'pl-docs' of https://github.com/Skysplit/yii2 into pl-docs
Update readme.md [ci skip]
Fix PHPDoc [skip ci]
Update polish messages [ci skip]
Merge pull request #5165 from Skysplit/pl-docs

[skip ci] Updated polish docs(README.md) and framework messages
Merge pull request #5163 from mrarthur/patch-8

Fix PHPDoc [skip ci]
Fixed changelog formatting
Fixes #5164: Added `Inlfector::$transliterator` that can be used to customize intl transliteration
Adjusted Russian translation of REST rate limiting guide
Ukrainian message translation
Merge pull request #5174 from arturf/ua_lang

[ci skip] Ukrainian message translation
Update UPGRADE.md
Fixes #5176: `ActiveFixture` will reset table in its `load()` method instead of `unload()`