Revert to root level package structure for stow

- Document xstow usage for systems lacking GNU Stow
- Add SPDX headers to .stowrc for license compliance
- Add REUSE specification compliance notes to README

git/.gitconfig

@@ -0,0 +1,9 @@
+# SPDX-FileCopyrightText: 2019, 2022 Kris Lamoureux <kris@lamoureux.io>
+# SPDX-License-Identifier: 0BSD
+
+[core]
+  editor = vim
+[init]
+  defaultBranch = main
+[include]
+  path = ~/.gitconfig_other