Add README

README.md

+xpra-sudo
+=========
+
+`xpra-sudo` is a wrapper script for Xpra that allows running the server as a
+different user on the same system using sudo.
+
+Installation
+------------
+
+Just copy both scripts (`xpra-sudo` and `xpra-sudo-ssh`) to a directory in your
+`PATH`. If you don't want `xpra-sudo-ssh` to mess up your path, you can also
+place it somewhere else and set the variable `SSH_HELPER` in `xpra-ssh`
+accordingly.
+
+Usage
+-----
+
+To start an Xpra session as user `user`, just run this command:
+
+    xpra-sudo start sudo:user:42 --start-child=urxvt
+
+How does it work?
+-----------------
+
+Xpra already supports connecting via SSH and `xpra-sudo` uses this mechanism:
+it passes `xpra-sudo-ssh` as a custom SSH command to Xpra using the `--ssh`
+option and changes `sudo:user:42` to `ssh:user@localhost+sudo:42`.
+`xpra-sudo-ssh` then recognizes the special hostname `localhost+sudo` and uses
+sudo instead of SSH to run the command.
+
+How does that sudoers syntax work again?
+----------------------------------------
+
+`xpra-sudo` works fine without the `NOPASSWD` option in sudo, but you might
+nonetheless set it for your convenience and don't remember the syntax? Here's
+my service for you, this allows the user `julian` to run commands as `user`:
+
+    julian ALL=(user) NOPASSWD: ALL