docs: added note about logo size

Author: berezinant

docs/topics/formats/dokka-html.md

@@ -222,6 +222,8 @@ you can [override the `logo-styles.css` stylesheet](#customize-styles) to custom
 For an example of how to do this, see our
 [custom format example project](https://github.com/Kotlin/dokka/tree/%dokkaVersion%/examples/gradle/dokka-customFormat-example).
 
+Note that the maximum supported logo dimensions are 120 px width and 36 px height. If you provide a larger image, it will be resized.
+
 ### Modify the footer
 
 You can modify text in the footer by using the `footerMessage` [configuration option](#configuration).