Clarification on need to register site with Valet

See #15 where we ran into 404 issues due to not having done a valet park in the directory the installation was done nor a `valet link`.

Author: jasperf

README.md

@@ -22,6 +22,8 @@ wp valet new <name> [--project=<project>] [--in=<dir>] [--version=<version>] [--
 This command will spin up a new WordPress installation -- complete with database and https
 _ready-to-use in your browser_ faster than you can put your pants on.
 
+**NB** If you have not used `valet park` for the directory or parent directory you are running the installation in you need to do a `valet link` to make sure the site will run without running into 404s.
+
 **OPTIONS**
 
 	<name>