Link DRY to wikipedia (#154)

refactoring/index.md

@@ -2,7 +2,7 @@
 
 Refactoring is very important in relation to these topics. Just as important as the other topics covered here, is how to take good code and turn it into great code.
 
-We can use [design patterns](../patterns/index.md) to DRY up code and generalize abstractions. We must avoid [anti-patterns](../anti_patterns/index.md) while we do this. While they may be tempting to employ, their costs outweigh their benefits.
+We can use [design patterns](../patterns/index.md) to [DRY] up code and generalize abstractions. We must avoid [anti-patterns](../anti_patterns/index.md) while we do this. While they may be tempting to employ, their costs outweigh their benefits.
 
 > Shortcuts make for long days.
 
@@ -13,3 +13,5 @@ We can also use [idioms](../idioms/index.md) to structure our code in a way that
 Tests are of vital importance during refactoring.
 
 ## Small changes
+
+[DRY]: https://en.wikipedia.org/wiki/Don%27t_repeat_yourself