README.md: Remove nesting version-control/git

There's no need to hard-code target directories in this repository.
Anyone consuming this material can use submodules and pick their own
target directory.

diff --git a/version-control/git/README.md b/README.md
similarity index 100%
rename from version-control/git/README.md
rename to README.md

diff --git a/version-control/git/cheat-sheet.md b/cheat-sheet.md
similarity index 100%
rename from version-control/git/cheat-sheet.md
rename to cheat-sheet.md

diff --git a/version-control/git/instructor.md b/instructor.md
similarity index 100%
rename from version-control/git/instructor.md
rename to instructor.md