Improve alt attribute text for images

Author: yasulab

_includes/navbar.html

@@ -1,7 +1,7 @@
 <header>
   <nav class="navbar navbar-expand-lg navbar-light bg-main fixed-top">
       <a class="navbar-brand" href="/#top">
-        <img src="/img/2023/logo_640x160.svg" width="290px" class="d-inline-block align-top" alt="ナビゲーション・アイコン">
+        <img src="/img/2023/logo_640x160.svg" width="290px" class="d-inline-block align-top" alt="DojoCon Japan 2023">
       </a>
       <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbar-nav"
         aria-controls="navbarNavAltMarkup" aria-expanded="false" aria-label="Toggle navigation">

index.md

@@ -7,7 +7,7 @@ layout: default
   </div>
   <div class='information'>
     <div class="theme">Be Cool</div>
-    <img src="/img/2023/logo_640x160.svg" alt='Cover Photo'>
+    <img src="/img/2023/logo_640x160.svg" alt='DojoCon Japan 2023 のロゴ画像'>
     <div class="event-date-and-location">
       <p>2023.8.27 Sun<br>at 奈良女子大学 Nara Women's University</p>
     </div>