Update .gitignore

[randomwangran]

Just for convenience.

[randomwangran]

Just a quick follow up with the motivation for this change:

I have your packages installed by git-submodule (ref).

The issue is that I often accidentally added some backup files or left some byte-compile file in the package folder.

This makes tracking the change within my main .emacs project really hard to identify what's going on.

If the user's git dashboard is clean, then it would be super easy to identify the changes over time.

I've attached a figure to show my clutter .emacs magit-status dashboard.

I really don't know how to solve it from my side, so I just did this awkward PR hoping the maintainer could help me.

Thanks for your awesome packages.