docs: Add tutswiki.com to the showcase

docs/content/showcase/tutswiki.md

@@ -0,0 +1,19 @@
+---
+lastmod: 2017-05-23
+date: 2017-05-23T07:33:00Z
+description: "Collaborative tutorials for the internet"
+license: ""
+licenseLink: ""
+sitelink: https://tutswiki.com/
+sourceLink: https://github.com/TutsWiki/source
+tags:
+- tutorial
+- wiki
+- computer science
+- programming
+- documentation
+- books
+thumbnail: /img/tutswiki-tn.jpg
+title: TutsWiki.com
+---
+