added resource links in context of relevant docs

Author: wion

_includes/index-lists-build.html

@@ -6,7 +6,7 @@
 
 * [Content types: core and custom](/build/content-types){: style="color:red;"} ([Issue 151](https://github.com/textpattern/textpattern.github.io/issues/151))
 * [Building site structures](/build/site-structures){: style="color:red;"} ([Issue 152](https://github.com/textpattern/textpattern.github.io/issues/152))
-* [Themes: Creating, using, and sharing](/build/themes-creating-using-and-sharing)
+* [Themes: Creating, using, and sharing](/build/themes-creating-using-and-sharing) [Themes site](https://themes.textpattern.com)
 {:.list--no-bullets style="list-style-position:inside; list-style-type:'- '"}
 
 </section>
@@ -17,7 +17,7 @@
 * [Planning website architecture](/build/planning-website-architecture){: style="color:red;"} ([Issue 156](https://github.com/textpattern/textpattern.github.io/issues/156))
 * [Installing, upgrading and using plugins](/build/plugins-installing-upgrading-and-using)
 * [Creating administration themes](/build/creating-administration-themes)
-* [Developing plugins](/development/)
+* [Developing plugins](/development/) [Plugins site](https://plugins.textpattern.com)
 {:.list--no-bullets style="list-style-position:inside; list-style-type:'- '"}
 
 </section>