chore: default values example in classes.md (#2133)
chore: default values example in classes.md (#2133)

* Update classes.md

* chore: add example of class with default props

Co-authored-by: Pavel Semyonov <9fef4c3b275d1b1cf2d37bb4fde2472935675f02@users.noreply.github.com>
hltj/kotlin-web-site-cn,JetBrains/kotlin-web-site,JetBrains/kotlin-web-site,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,hltj/kotlin-web-site-cn,JetBrains/kotlin-web-site,hltj/kotlin-web-site-cn,JetBrains/kotlin-web-site,JetBrains/kotlin-web-site,JetBrains/kotlin-web-site,hltj/kotlin-web-site-cn