docs: Update README with CLI arguments

README.md

@@ -4,6 +4,12 @@
 
 This is a simple CLI you can use to continuously update an A DNS record for a domain using CloudFlare's free DDNS service.
 
-# TODO
+## Options
 
-Write about usage and CloudFlare setup
+```
+    -k, --key <auth-key>     The auth key you need to generate in your Cloudflare profile
+    -c, --cache <cache>      Cache file for previously reported IP address (if skipped the IP will be reported on every execution)
+    -d, --domain <domain>    The domain for which you want to report the current IP address
+    -e, --email <email>      Your Cloudflare login email
+    -z, --zone <zone>        The zone in which your domain is (usually that is your base domain name)
+```

src/main.rs

@@ -19,7 +19,7 @@ struct Cli {
     #[structopt(long = "key", short = "k")]
     auth_key: String,
 
-    /// The zone in which your domain is (usually that is your domain without the subdomain)
+    /// The zone in which your domain is (usually that is your base domain name)
     #[structopt(long = "zone", short = "z")]
     zone: String,