bootstrap.sh self-elevates with sudo; USB install docs rewritten

bootstrap.sh: add self-elevation — if not root, re-exec under sudo.
Double-clicking the script in GNOME ("Run in Terminal") now prompts for
the sudo password automatically, no extra commands needed.

README: rewrite USB section around the real workflow:
  - clone with "Open in Terminal" from the file manager sidebar
  - Option A: right-click folder → Open in Terminal → sudo ./setup.sh
  - Option B: double-click bootstrap.sh → "Run in Terminal?" → sudo prompt
  - note on nautilus-extension-gnome-terminal and exFAT vs ext4

https://claude.ai/code/session_017WJtGcE5jjerAQCUBWUE3H

bootstrap.sh

@@ -4,12 +4,20 @@
 # One command to paste into a new Ubuntu box:
 #   curl -fsSL https://raw.githubusercontent.com/outis1one/ubuntu-post-install/main/bootstrap.sh | sudo bash
 #
+# Or double-click it in the file manager ("Run in Terminal") — it will
+# prompt for your sudo password automatically.
+#
 # What it does:
 #   1. Installs git if missing (the only hard dependency)
 #   2. Clones (or updates) the repo to ~/ubuntu-post-install
 #   3. Launches the interactive setup wizard
 set -euo pipefail
 
+# Self-elevate: if not root, re-exec under sudo so a plain double-click works.
+if [ "${EUID:-$(id -u)}" -ne 0 ]; then
+    exec sudo bash "$0" "$@"
+fi
+
 REPO_URL="https://github.com/outis1one/ubuntu-post-install.git"
 DEST="${HOME:-/root}/ubuntu-post-install"