Create UPDATING.md

UPDATING.md

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+### Updating Shairport Sync
+This guide is for updating an installation of Shairport Sync you built yourself. If you installed Shairport Sync from a package, these instructions don't apply. 
+
+To do an update, you basically have to go through the whole process of building Shairport Sync again,
+but a few steps are shorter because you've done them before; you won't have to reinstall the build tools or libraries needed, and you won't have to define the user and group or reconfigure the settings in the configuration file.
+
+But before you begin, you should update and upgrade any packages.
+
+Here is the sequence for Raspbian Jessie, which is based on Debian Jessie. The same commands work for Ubuntu, and maybe more. Here, a non-`root` user with `sudo` privileges is assumed.
+
+```
+$sudo apt-get update
+$sudo apt-get upgrade
+```
+Next, stop playing music to your device.
+
+Now, to update and install Shairport Sync, if you still have the directory in which you previously built Shairport Sync, navigate your way to it and execute the command:
+```
+$git pull
+```
+Otherwise, just pull Shairport Sync from `github` again and move into the new directory:
+```
+$git clone https://github.com/mikebrady/shairport-sync.git
+$cd shairport-sync
+```
+Now, while in the `shairport-sync` directory, perform the following commands (note that there is a choice you must make in there):
+```
+$autoreconf -fi
+
+#The following is the standard configuration for a Linux that uses the systemd initialisation system:
+$./configure --with-alsa --with-avahi --with-ssl=openssl --with-metadata --with-soxr --with-systemd
+#OR
+#The following is the standard configuration for a Linux that uses the older System V initialisation system:
+$./configure --with-alsa --with-avahi --with-ssl=openssl --with-metadata --with-soxr --with-systemv
+
+$make
+$sudo make install
+```
+At this point you have downloaded, compiled and installed the updated Shairport Sync. However, the older version is still running. So, you need to do a little more: 
+
+If you are on a `systemd`-based system such as Raspbian Jessie or recent versions of Ubuntu and Debian, execute the following commands:
+```
+$sudo systemctl daemon-reload
+$sudo systemctl restart shairport-sync
+```
+Otherwise execute the following command:
+```
+$sudo service shairport-sync restart
+```
+
+That's it. Your Shairport Sync should be upgraded now.