Adds _x() context for sprintf() text in bp_docs_get_item_term_id()

Fixes #322

includes/functions.php

@@ -157,7 +157,7 @@ function bp_docs_get_item_term_id( $item_id, $item_type, $item_name = '' ) {
 		}
 
 		$item_term_args = apply_filters( 'bp_docs_item_term_values', array(
-			'description' => sprintf( __( 'Docs associated with the %1$s %2$s', 'bp-docs' ), $item_type, $item_name ),
+			'description' => sprintf( _x( 'Docs associated with the %1$s %2$s', 'Description for the associated-item taxonomy term. Of the form "Docs associated with the [item-type] [item-name]" - item-type is group, user, etc', 'bp-docs' ), $item_type, $item_name ),
 			'slug'        => $item_term_slug,
 		) );