Update updated documentation section

Amanda Butler · web-flow · commit 9abdfe94ac2d · 2019-01-10T04:08:22.000-06:00
Add link to updated contributing guide.
diff --git a/docs/introduction/introduction.md b/docs/introduction/introduction.md
@@ -84,6 +84,7 @@ Please see the following sections of our documentation for more information.
 
 ### Recently updated documentation
 
+* An updated [contributing guide](../contributing/index.html).
 * A revised [porting guide](../porting/index.html).
 * A [review of the full process of taking a project to production](./evaluation-production/index.html).
 * An updated [quick start](../quick-start/index.html) to demonstrate more Mbed OS capabilities.
