Can I add a little text here in Register.template.php for explaining?
echo '
<form action="', $scripturl, '?action=register2" method="post" accept-charset="UTF-8" name="registration" id="registration" onsubmit="return verifyAgree();">
<h2 class="category_header">', $txt['registration_form'], '</h2>
<h3 class="category_header">', $txt['required_info'], '</h3>
<div class="windowbg2">
<input type="password" name="autofill_honey_pot" style="display:none" />
<fieldset class="content">
<dl class="register_form">
<dt>
<strong><label for="elk_autov_username">', $txt['username'], ':</label></strong>
</dt>
<dd>
<input type="text" name="user" id="elk_autov_username" size="30" tabindex="', $context['tabindex']++, '" maxlength="25" value="', isset($context['username']) ? $context['username'] : '', '" class="input_text" placeholder="', $txt['username'], '" required="required" autofocus="autofocus" />
<span id="elk_autov_username_div" style="display: none;">
<a id="elk_autov_username_link" href="#">
<img id="elk_autov_username_img" src="', $settings['images_url'], '/icons/field_check.png" alt="*" />
</a>
</span>
</dd>
A break after this?
<strong><label for="elk_autov_username">', $txt['username'], ':</label></strong>