Document Android keyboard shortcuts

Android app keyboard shortcuts are very useful for ChromeOS users, and the Android version does appear to have some. For example, Ctrl+F jumps ahead 10 seconds. This isn't revealed in any user documentation, however, nor is it the same shortcut that is documented for desktop versions. It would be really handy to provide user documentation listing all keyboard shortcuts provided in the Android version, and better yet to provide a means to customize them.