Notable Updates to 2270 Git Repository

Jan 20: Added text and video cheat sheets on how to use Linux and the command line. This is relevant if you are using the Virtual Box VM.
Jan 23: Added linked_list.cpp to lectures/ folder. This is what I typed in class.
Jan 27: Added email_policy.md to main dir
Jan 27: Uploaded hw 2
Jan 30: Updated Python impl definition for HW2. It wasn't even valid Python syntax.