Install a proper #!/bin/sh style rc.local on Void Linux

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

contrib/void/rc.local

@@ -0,0 +1,7 @@
+#!/bin/sh
+# This script is executed once at boot, at the very end,
+# right before starting the TTYs.
+#
+# Each line is run in sequence.
+#
+# NOTE: Remeber to set the executable bit!