Updated readme to clarify use on non-raspbian distributions is not advised

README.md

@@ -1,6 +1,33 @@
 # rpi-update
 
-An easier way to update the firmware of your Raspberry Pi.
+An easier way to get the latest firmware for your Raspberry Pi.
+
+# Notes
+
+This is only intended for use with Raspbian. If you are using a different
+distribution then check with the maintainers if using rpi-update is safe.
+
+If the distribution ships a custom kernel, then it almost certainly is not
+safe. Also differences in the usage of /boot and /opt/vc directories will
+likely make it unsafe.
+
+Even on Raspbian you should only use this with a good reason.
+
+This gets you the latest bleeding edge kernel/firmware.
+There is always the possibility of regressions.
+
+Bug fixes and improvements will eventually make their way into new Raspbian
+releases and apt-get when they are considered sufficiently well tested.
+
+A good reason for using this would be if you like to help with the testing effort,
+and are happy to risk breakages and submit bug reports. These testers are welcome.
+
+Also if you are suffering from a bug in current firmware (perhaps as one of
+the reporters of the bug on github or forum) and a fix has been pushed out for
+testing, then using rpi-update is the right way to get the fix until it makes
+its way into new Raspbian images and apt-get.
+
+Backing up before updating is always advisable.
 
 ## Installing
 
@@ -95,6 +122,13 @@ Allows you to delete unused module directories when doing an update. Set it equa
 
 will remove previously installed module files. Use this option to free disk space used by older module updates.
 
+#### `JUST_CHECK`
+
+To just get a list of commits contained in rpi-update since you last updated, run:
+
+    sudo JUST_CHECK=1 rpi-update
+
+This won't update your firmware
 
 #### Troubleshooting