Update styles docs

Fixes #1691

editions/tw5.com/tiddlers/howtos/Using Stylesheets.tid

@@ -1,5 +1,5 @@
 created: 20140305091244145
-modified: 201804111739
+modified: 20210104090402829
 tags: [[Customise TiddlyWiki]]
 title: Using Stylesheets
 type: text/vnd.tiddlywiki
@@ -30,6 +30,8 @@ body.tc-body {
 }
 ```
 
+You can then use your own [[styles and classes in WikiText|Styles and Classes in WikiText]].
+
 !! Additional Resrouces
 
 * [[Cascading Style Sheets (CSS) at mozilla|https://developer.mozilla.org/en-US/docs/Web/CSS]]