added git-game link

* added statement to explicitly state where to look for the next clue: 
**You should always check the README.md file for your next clue!**
* updated all README's to suggested writing style (Your writing style is a lot nicer than what we were doing. I'll definitely use this more often)
* fixed `who's` grammar mistake to `whose`
* removed unrelated text in `.gitignore` file
* corrected `abstract data structure` to `abstract data type`
* fixed  `the executable "outputclue"` to `the bash script outputclue.sh`  (each occurrence)
* explicitly stated there is a bug when merging and it needs to be fixed
* made diff on files more explicit, file is now 50k lines, 100k words, which prevents people from accidentally finding the solution.
* placed all information in the keyboard branch into the Henry branch (keyboard wasn't really needed)
* explicitly state to update master (also removed merge conflict). and is updated from forked repository

suggestions from: #646 

Here is a game made by previous students to test your git skills:

https://github.com/hgarc014/git-game.git