Remove reference to syncisos from readme

The readme instructs the user to run:
./manage.py syncisos
But this custom function no longer exists and therefore generates an
error.
This commit removes the reference from the readme.

README.md

@@ -72,7 +72,6 @@ packages, you will probably want the following:
         # Package file listing
         wget http://mirrors.kernel.org/archlinux/core/os/x86_64/core.files.tar.gz
         ./manage.py reporead --filesonly x86_64 core.files.tar.gz
-        ./manage.py syncisos
 
 Alter architecture and repo to get x86\_64 and packages from other repos if
 needed.