feat: add opengraph (#120)

Author: MBP16

index.html

@@ -6,6 +6,11 @@
       name="viewport"
       content="width=device-width, initial-scale=1, maximum-scale=1, shrink-to-fit=no, viewport-fit=cover" />
     <meta name="theme-color" content="#F9F0F0" />
+    <meta property="og:title" content="OTL - Online Timetable with Lectures" />
+    <meta property="og:description" content="카이스트 학생들을 위한 시간표 서비스입니다" />
+    <meta property="og:type" content="website" />
+    <meta property="og:site_name" content="OTL" />
+    <meta property="og:image" content="https://otl.kaist.ac.kr/static/favicon-192.png" />
     <!--
       manifest.json provides metadata used when your web app is added to the
       homescreen on Android. See https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/