Keyboard shortcut (may be Ctrl+M, like in some KDE applications) and right-click menu option to hide the menu bar. This menu has too little items but takes too much place on the screen. (BTW, though it is insignificant detail, but may be it's also reasonable to move "Docsets..." item to 'File' or 'Edit' menu to not have 'Tools' menu with just one item)
May be also add "hamburger menu button" instead to the right side of the tab bar.
Full screen mode like in browsers may also be useful. There is never too much space on the screen when reading documentation :)