Include basic usage info in README

README.md

@@ -10,10 +10,20 @@ the `cwd`; it is expected to have a single email address per line.
 If the environment variable `WATCHDOG_LOG` is set, all output will be
 redirected there.
 
+**NOTE** Currently only useful for services running over HTTP
+
 
 ## Dependencies
 
 - curl:  Polling the servers
 - msmtp: Sending email; requires separate configuration
 
-**NOTE** Currently only useful for services running over HTTP
+
+## Usage
+
+Create the following files in the script directory:
+
+- `urls`
+  - One url per line
+- `recipients`
+  - One email address per line