add blurb about contributing to landing page (#112)

* add blurb about contributing

* make it better 🍍

* make it better, again 🍍

* fix backwards link markdown syntax

wiki/landing-page/en.md

@@ -3,6 +3,8 @@
 This site houses heavily work-in-progress documentation for developing with projects in the Quilt ecosystem.
 Check the sidebar to see what articles are currently available!
 
+If you are looking to contribute, [this is a great place to start as it lists missing and partially completed wiki articles](https://github.com/QuiltMC/developer-wiki/issues/69).
+
 Keep in mind that when modding with Quilt, this isn't the only source of documentation you can use.
 Here are a few other places to look if you're not seeing what you need: