Updated hw4-contributing/README.md
Merge pull request #479 from jfan013/cs100-2014fall

Fixed typo and added a line for readability
Merge pull request #490 from gbrlrz017/cs100-2014fall

Updated README.md files in assignments to include test script instructions.
removed the picture in shell-trickes
Merge pull request #509 from ChemicalWonders/cs100-2014fall

removed the picture in shell-tricks