Add entry to example README

Author: LegNeato

examples/README.md

@@ -120,6 +120,7 @@ Example | File | Description
 `logs` | [`app/logs.rs`](./app/logs.rs) | Illustrate how to use generate log output
 `plugin` | [`app/plugin.rs`](./app/plugin.rs) | Demonstrates the creation and registration of a custom plugin
 `plugin_group` | [`app/plugin_group.rs`](./app/plugin_group.rs) | Demonstrates the creation and registration of a custom plugin group
+`random` | [`app/random.rs`](./app/random.rs) | Show how to use a central source of entropy for random number generation.
 `return_after_run` | [`app/return_after_run.rs`](./app/return_after_run.rs) | Show how to return to main after the Bevy app has exited
 `thread_pool_resources` | [`app/thread_pool_resources.rs`](./app/thread_pool_resources.rs) | Creates and customizes the internal thread pool