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

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    leopard (0.1.7)
+    leopard (0.2.1)
       concurrent-ruby (~> 1.1)
       dry-configurable (~> 1.3)
       dry-monads (~> 1.9)
@@ -53,7 +53,7 @@ GEM
     racc (1.8.1)
     rainbow (3.1.1)
     rake (13.3.0)
-    regexp_parser (2.11.0)
+    regexp_parser (2.11.1)
     reline (0.6.2)
       io-console (~> 0.5)
     rubocop (1.79.2)

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