To customize it in your jira;
1. Go to Administration > System > General Configuration
2. Click Edit Configuration
3. Paste your html code in the introduction section.
4. Click Udpate.
4. The introduction has changed!
Here is an html example:
<!DOCTYPE html>
<head>
</head>
<body>
</body>
<table>
<tr>
<td><img src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwLO_gHWG7Vj4Rmbc8lVZe8XiIBwg3LdB5bWzmthyphenhyphen1li-NxW6tdouwK2NqXiPf5_cpUU0LxD2hMDvcJAAaY6kjjcQoO7wYaY8F520p1Gaqzf9mCBAMOwA0BcSUEtZj31R9NaDoYYVcUCDJ/s1600/logo.png" width="250" height="150"/> </td>
<td><h3>Johnson Controls' e Hosgeldiniz</h3>
<p>Johnson Controls, global olarak teknoloji ve 150'den fazla ulkedeki hizmet veren end lideridir.</p></td>
</tr>
</table>
</html>
