Add Infomation about adding Icons to Tabs in YAML Files

[Deleted user]

Opened this as per Luke's request.

See github Issue: octobercms/october#3856 (comment)

Add another section under this section found here: https://octobercms.com/docs/backend/forms#form-tab-options

YAML File Example:

tabs:
     icons:
         0: icon-camera-retro
         1: icon-diamond
         2: icon-crosshairs

To HTML File Example:

<div class="control-tabs responsive-tabs" data-control="tab">
    <ul class="nav nav-tabs">
        <li class="active"><a href="#contentTabOne"><i class="icon-camera-retro"></i><br>One</a></li>
        <li><a href="#contentTabTwo"><i class="icon-diamond"></i><br>Two</a></li>
        <li><a href="#contentTabThree"><i class="icon-crosshairs"></i><br>Three</a></li>
    </ul>
    <div class="tab-content">
        <div class="tab-pane active">
            Tab one content
        </div>
        <div class="tab-pane">
            Tab two content
        </div>
        <div class="tab-pane">
            Tab three content
        </div>
    </div>
</div>

[Deleted user]

Closing this due to already been fixed as per this issue: #330