Add configuration for git

- Add .config/git/config
  + Define aliases
  + Configure default behavior in various situations
  + Add user information with signing key
- Add .config/git/commit_msg_template.txt
- Add .config/git/ignore
- Integrate `git` aliases into the shell

.zshrc

@@ -91,6 +91,10 @@ zstyle ':completion:*:messages' format '%d'
 zstyle ':completion:*:warnings' format 'No matches for: %d'
 zstyle ':completion:*' group-name ''
 
+# Make `git` sub-commands in ~/.local/bin completable
+zstyle ':completion:*:*:git:*' user-commands \
+    ${${${(M)${(k)commands}:#git-*}#git-}:#(receive-pack|upload-pack|upload-archive|shell)}
+
 
 # Jump to frequently used directories with `z <fragment>`
 if _command_exists zoxide; then