improve
Update tutorial-advanced-app.md
Grammar fix

Minor words order fix.
Fixed typos [skip ci]
Merge pull request #6091 from nikbas/formatter-fix

Fixed typos in formatter guide
Merge pull request #6086 from artyhedgehog/patch-1

Grammar fix
Fixed `yii\mongodb\ActiveRecord` saves `null` as `_id`, if attributes are empty
some typos and grammar for Gii
Merge pull request #6078 from pabloassembler/patch-1

Update tutorial-advanced-app.md
Merge pull request #6076 from mirjalal/master

improve
ensure apidoc works with relative paths
add guidePrefix option for apidoc
Update README.md