README: coding style: allow 120ch

I like the good ol' days of teletypes, but not that much...
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

README.md

@@ -89,9 +89,14 @@ Currently there is a mix of indentation styles so any changes to
 existing files should be consistent with the existing style. For new
 files:
 
-  - C: please use standard linux-with-tabs
+  - C: please use standard linux-with-tabs, see Linux kernel
+    doc Documentation/process/coding-style.rst
   - Shell: use TABs for indentation
 
+Exceptions:
+
+  - While the kernel standard requires 80 columns, we allow up to 120.
+
 ## Patches
 
 Patches are welcome at the KVM mailing list <kvm@vger.kernel.org>.