Create [archive_description] shortcode to use in category-description template part

[bobbingwide]

Requirement

Create a shortcode to be used to implement contents for the category-description template part.

Solution

• [x] Name the shortcode [archive_description].
• [x] Use term_description() to obtain the description.
• [x] Implement for tags, categories and custom taxonomies.

[bobbingwide]

This shortcode is no longer necessary. It can be removed.