Document Linux kerenel version requirements

README.md

@@ -29,8 +29,9 @@ capabilities, so these can continue to be used by containers.
 
 To run weave on a host, you need to install...
 
-1. docker. We've tested with versions 0.9.1 through 1.2.0, but other
-   versions should work too.
+1. Linux and Docker. We've tested with Docker versions 0.9.1 through
+   1.2.0, but other versions should work too. Linux kernels after 3.5
+   are known to work; the newer the better.
 2. weave. Install this with
 
         sudo wget -O /usr/local/bin/weave \