feat(git): add comprehensive git folder management commands and update documentation

bin/clean-git-folder

@@ -1,7 +1,12 @@
 #!/usr/bin/env bash
 
 clean-git-folder() {
-    local git_folders=$(ls-git-folder)
+    if [[ -z "$1" ]]; then
+        echo '$1/path is empty.'
+        exit
+    fi
+
+    local git_folders=$(ls-git-folder "$1")
     for git_folder in $git_folders; do
         echo "Clean git folder $git_folder."
         git -C "$git_folder" clean -df