Adding Attribute to all categories

Question

I'm looking to add an optional attribute to a category page in Magento. I found this question to be very helpful although I can't seem to have my desired drop down option appear on screen.

Rather than creating a module, I'm attempting to extend the view in my current theme. I have edited the file <magento-root>/app/design/adminhtml/<vendor>/<theme>/Magento_Catalog/ui_component/category_form.xml to look like the following:

(it was mocked after the category tab within the category page in the magento admin, just to be a proof of concept)

<?xml version="1.0" encoding="UTF-8"?>
<form xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
    <fieldset name="category.attributes">
        <argument name="data" xsi:type="array">
            <item name="config" xsi:type="array">
                <item name="label" xsi:type="string" translate="true">Custom Attributes</item>
                <item name="collapsible" xsi:type="boolean">true</item>
                <item name="sortOrder" xsi:type="number">10</item>
            </item>
        </argument>
        <field name="description">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="class" xsi:type="string">Magento\Catalog\Ui\Component\Category\Form\Element\Wysiwyg</item>
                    <item name="formElement" xsi:type="string">wysiwyg</item>
                    <item name="wysiwygConfigData" xsi:type="array">
                        <item name="settings" xsi:type="array">
                            <item name="theme_advanced_buttons1" xsi:type="string">bold,italic,|,justifyleft,justifycenter,justifyright,|,fontselect,fontsizeselect,|,forecolor,backcolor,|,link,unlink,image,|,bullist,numlist,|,code</item>
                            <item name="theme_advanced_buttons2" xsi:type="boolean">false</item>
                            <item name="theme_advanced_buttons3" xsi:type="boolean">false</item>
                            <item name="theme_advanced_buttons4" xsi:type="boolean">false</item>
                            <item name="theme_advanced_statusbar_location" xsi:type="boolean">false</item>
                        </item>
                        <item name="files_browser_window_url" xsi:type="boolean">false</item>
                        <item name="height" xsi:type="string">100px</item>
                        <item name="toggle_button" xsi:type="boolean">false</item>
                        <item name="add_variables" xsi:type="boolean">false</item>
                        <item name="add_widgets" xsi:type="boolean">false</item>
                        <item name="add_images" xsi:type="boolean">false</item>
                    </item>
                    <item name="template" xsi:type="string">ui/form/field</item>
                    <item name="source" xsi:type="string">category</item>
                    <item name="wysiwyg" xsi:type="boolean">true</item>
                    <item name="dataScope" xsi:type="string">description</item>
                    <item name="sortOrder" xsi:type="number">51</item>
                    <item name="rows" xsi:type="number">8</item>
                </item>
            </argument>
        </field>
    </fieldset>
</form>

I have cleared my <magento-root>/var folder and cleaned my cache. Being new to magento & magento 2, can anyone give me a pointer on what I'm missing conceptually? I can view the original category_form.xml file and notice the current tabs in the category page within the magento admin (products -> categories). I'm attempting to append to the current xml with no luck afterwards. Any help is greatly appreciated!