Update the README

Remove referenced to developing on the host, we shouldn't support it.

Move script/validate to scripts/validate to be consistent.
Set the default target to be binary instead of clean.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

scripts/validate/check-git-diff

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+set -eu
+
+DIFF_PATH=$1
+
+if [ "`git status --porcelain -- $DIFF_PATH 2>/dev/null`" ]; then
+    echo
+    echo "These files were changed:"
+    echo
+    git status --porcelain -- $DIFF_PATH 2>/dev/null
+    echo
+    exit 1
+else
+    echo "$DIFF_PATH is correct"
+fi;