Added two more missing tooltips

Author: shinzlet

ui.html

@@ -12,11 +12,11 @@
 	    <header id="options">
 		<div id="logo" aria-hidden="true">Oildrop</div>
 		<div class="bar dense-bar">
-		    <label>
+		    <label title="Toggle between Oildrop's light and dark mode.">
 			<input id="light-toggle" class="wrapped-checkbox" type="checkbox">
 			<div class="checkbox-proxy" id="light-toggle-icon"></div>
 		    </label>
-		    <button id="settings-button"></button>
+		    <button id="settings-button" title="Open the settings dialogue, which contains additional features and accessibility options."></button>
 		</div>
 	    </header>