Saved from https://rudrastyh.com/wordpress/add-custom-fields-to-taxonomy-terms.html

add_field_new_term_screen

add_action( 'post_tag_add_form_fields', 'mk_add_term_fields' );

function mk_add_term_fields( $taxonomy ) {

	echo '<div class="form-field">
	<label for="term-field-key">Text Field</label>
	<input type="text" name="term-field-key" id="term-field-key" />
	<p>Field description may go here.</p>
	</div>';

}

// post_tag/category/custom_tax_name - change in hook
//taxonomy fed through in function