adding manifest.json and related

index.html

@@ -1,5 +1,5 @@
 <!DOCTYPE html>
-<html>
+<html lang="en">
   <head>
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1">
@@ -7,6 +7,7 @@
     <link id="shortcut-icon" rel="shortcut icon" href="img/logo32x32.png" />
     <!-- Browser styling for Chrome, FF, Opera -->
     <meta name="theme-color" content="#3949AB">
+    <link rel="manifest" href="/manifest.json">
     <!-- Google's Roboto font -->
     <link href="https://fonts.googleapis.com/css?family=Roboto:300,400,400italic,500,700&subset=latin,cyrillic"
       rel="stylesheet" type="text/css" />