Add sudo and su.

Fixes #150.

README.md

@@ -151,6 +151,8 @@ Notes:
 - For a simple web server for all files in the current directory (and subdirs), available to anyone on your network, use:
 `python -m SimpleHTTPServer 7777` (for port 7777 and Python 2) and `python -m http.server 7777` (for port 7777 and Python 3).
 
+- For running a command with privileges, use `sudo` (for root) or `sudo -u` (for another user). Use `su` or `sudo bash` to actually run a shell as that user. Use `su -` to simulate a fresh login as root or another user.
+
 
 ## Processing files and data