Add example config.json file to README.md

Author: JesseEstum

README.md

@@ -290,6 +290,25 @@ separate configuration file. We use `config/toxiproxy.json`. This file can be
 passed to the server using the `-config` option, or loaded by the application
 to use with the `populate` function.
 
+An example `config/toxiproxy.json`:
+
+```json
+[
+  {
+    "name": "web_dev_frontend_1",
+    "listen": "[::]:18080",
+    "upstream": "webapp.domain:8080",
+    "enabled": true
+  },
+  {
+    "name": "web_dev_mysql_1",
+    "listen": "[::]:13306",
+    "upstream": "database.domain:3306",
+    "enabled": true
+  }
+]
+```
+
 Use ports outside the ephemeral port range to avoid random port conflicts.
 It's `32,768` to `61,000` on Linux by default, see
 `/proc/sys/net/ipv4/ip_local_port_range`.