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

bin/add-git-folder

@@ -0,0 +1,32 @@
+#!/bin/bash
+
+add-git-folder() {
+    if [[ -z "$1" ]]; then
+        echo '$1/branch is empty.'
+        exit
+    fi
+    if [[ -z "$2" ]]; then
+        echo '$2/url is empty.'
+        exit
+    fi
+    if [[ -z "$3" ]]; then
+        echo '$3/path is empty.'
+        exit
+    fi
+
+    # Add to .gitmodules
+    git submodule add -f -b "$1" "$2" "$3"
+
+    # Ensure branch is Odoo version
+    git -C "$3" switch "$1"
+
+    # Save version
+    save-version
+
+    # Restore staged submodule files
+    git restore --staged .gitmodules "$3"
+
+    # Remove from working tree
+    # rm -rf .git/modules/"$2" || true
+    # git rm --cached "$2" || true
+}