Update README, update mirror output, update test_mirror to reflect changes in mirror

[alyciakb]

• First draft of our updated README. Includes install and usage instructions, plus package dependencies. Please review (especially your functions) and make changes as needed.
• Install and package has been tested in my console and works. Please check to make sure it works in your console.
• Updated mirror.py to include the original image in the output array
• Updated test_mirror.py to reflect changes in the mirror function and changes in the output array size.

[everittB]

For the install instructions they differ from what was provided in Milestone2 guideline, pip install git+PACKAGE_URL.git, I will see if installing it this way works as well.

[alyciakb]

• Install works both ways, but changed the install directions to be in compliance with the milestone2 directions. Added the changes to the Update function documentation, minor changes to README pull request