A way to easy show diff between init.example.el and .doom.d/init.el

Hi,

Today I've merged upstream and the `make` command removed the neotree package for me. I was very confused why would that happen. After an hour debugging and manually bisect the git log, I found out that you've moved the neotree package from `:tools` to `:ui`, and of cause you updated the init.example.el file accordingly.

The thing is, my ~/.doom.d/init.el still has neotree under `:tools` section, such that the package management script will not be able to discover the new change thus removed it.

The problem was solved for me, but it raise a question, would it be nice to have a default short-cut key to open a Ediff session on those two init files? This at least encourage people to check the difference between the two more often.

In Spacemacs there is a key mapping `SPC f e d` for this exact purpose, I would highly recommend to implement a similar function for this. Thank you.