remove cached gitignore files

Sometimes I'll add things to my .gitignore after the fact as my needs change.

Removing these files from the git cache will allow the .gitignore to ignore them going forward when you make commits.

I found this StackOverflow answer when struggling to remember the caching that git uses. Code below, answer is here

# do the cache removal on folders if you have submodules
# I found the submodule updates were annoying to re-add
# so just do it one by one for big submodule repos

git rm -r --cached .
git add .
git commit -m "Drop files from .gitignore"