docs: Adds an example showing how to use groups (nested) (#32)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: bougyman <6848+bougyman@users.noreply.github.com>

Author: bougyman

examples/groups.rb

@@ -0,0 +1,32 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require_relative '../lib/leopard/nats_api_server'
+
+# Example to echo the given message
+class ServiceGroups
+  include Rubyists::Leopard::NatsApiServer
+
+  def initialize(a_var: 1)
+    logger.info "ServiceGroups initialized with a_var: #{a_var}"
+  end
+
+  group :mammal
+  group :feline, group: :mammal, queue: :meow
+  endpoint(:sound, group: :feline) { |msg| Success("Meow! #{msg.data}") }
+  endpoint(:fail, group: :feline) { |msg| Failure({ reason: 'cat nap', data: msg.data }) }
+end
+
+if __FILE__ == $PROGRAM_NAME
+  SemanticLogger.default_level = :info
+  SemanticLogger.add_appender(io: $stdout, formatter: :color)
+  ServiceGroups.run(
+    nats_url: 'nats://localhost:4222',
+    service_opts: {
+      name: 'example.groups',
+      version: '1.0.0',
+      instance_args: { a_var: 2 },
+    },
+    instances: 1,
+  )
+end