Update readme.md

readme.md

 # CS 349 Demo Code
 
-See the [course website](https://www.student.cs.uwaterloo.ca/~cs349/f17/) for the lecture slides associated with these demos: 
+* [X Windows](x/)
 
 
+See the [course website](https://www.student.cs.uwaterloo.ca/~cs349/f17/) for the lecture slides associated with these demos.
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 Bugs? Missing files? Fixes? Post to [Piazza](https://piazza.com/class/j6p05nk8vs52rt) with `lectures` tag.
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