It's not the same, those docs refers to qweb templates in other scenarios like reports and qweb, your situation involve qweb templates for js views and there are some diferences.
In your custom module you need to create an xml file for define the client qweb templates, new or extensions in a path below /static/ conventions use /static/src/xml/
In that file you need to define your templates definitions. For your case you could just copy and paste the original template to change it in place like:
<?xml version="1.0" encoding="UTF-8"?>
<templates id="template" xml:space="preserve">
<t t-name="ClientDetails">
<section class='client-details'>
<div class='client-picture'>
<img t-att-src='widget.partner_icon_url(partner.id)' />
</div>
<div class='client-name'><t t-esc='partner.name' /></div>
<div class='edit-buttons'>
<div class='button edit'><i class='fa fa-pencil-square' /></div>
</div>
<div class='client-details-box clearfix'>
<div class='client-details-left'>
<div class='client-detail'>
<span class='label'>Address</span>
<span class='detail client-address'><t t-esc='partner.address' /></span>
</div>
<div class='client-detail'>
<span class='label'>Email</span>
<span class='detail client-email'><t t-esc='partner.email' /></span>
</div>
<div class='client-detail'>
<span class='label'>Phone</span>
<t t-if='partner.phone'>
<span class='detail client-phone'><t t-esc='partner.phone' /></span>
</t>
<t t-if='!partner.phone'>
<span class='detail client-phone empty'>N/A</span>
</t>
</div>
</div>
<div class='client-details-right'>
<div class='client-detail'>
<span class='label'>Barcode</span>
<t t-if='partner.ean13'>
<span class='detail client-id'><t t-esc='partner.ean13'/></span>
</t>
<t t-if='!partner.ean13'>
<span class='detail client-id empty'>N/A</span>
</t>
</div>
<div class='client-detail'>
<span class='label'>Tax ID</span>
<t t-if='partner.vat'>
<span class='detail vat'><t t-esc='partner.vat'/></span>
</t>
<t t-if='!partner.vat'>
<span class='detail vat empty'>N/A</span>
</t>
</div>
</div>
</div>
</section>
</t>
</templates>
next you need to register that file to be loaded in the __openerp__.py under the key 'qweb'.
This only will change the widget visually, if you need to change some other behavior you will need to do it using js widget inheritance.