Added stash commands to gitconfig

FYI,

Stash is super handy, if you are on the wrong branch you can put all changes onto a temporary stack do something and bring it back. I use it a lot, for example, when I forgot to create a new branch. I'm still on master but started working on things. Then I do

• git stash clear to make sure there isn't anything anymore on my temporary stack
• git stash to move all current changes onto this temporary stack
• do something, like creating and changing the branch
• git stash apply to apply the edits from the temporary stack back onto the code

With this MR it would be able to do instead

• g sc
• g st
• g sa