nested git repos make dan want to drink before noon

facepalm.sh

# create the top-level project:
mkdir superproject
cd superproject
touch hello
git init .
git add .
git ci -m 'initial'

# create a git repo inside that:
mkdir subproject
cd subproject
touch hello-subproject
git init .
git add .
git ci -m 'initial (subproject)'
cd ..

# if you add everything to the index, like this:
git add .

# Now git treats 'subproject' like a submodule:
git submodule status

# make git forget subproject (undo `git add`):
git reset HEAD subproject

# verify it's untracked:
git st

# if you add the directory like this (with trailing slash):
git add subproject/

# then you can add the non-git files. See:
git st
git ls-files