Add example of multi registration in threaded env

examples/multi/threaded.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+require_relative '../../lib/tty-spinner'
+
+def spinner_options
+  [
+    ":spinner \e[1mNo\e[0m :number Row :line",
+    format: :dots,
+    error_mark: '✖',
+    success_mark: "\e[1m\e[32m✓\e[0m\e[0m"
+  ]
+end
+
+spinners = TTY::Spinner::Multi.new(*spinner_options)
+threads = []
+
+20.times do |i|
+  threads << Thread.new do
+    spinner = spinners.register(*spinner_options)
+    sleep Random.rand(0.1..0.3)
+
+    10.times do
+      sleep Random.rand(0.1..0.3)
+      spinner.update(number: "(#{i})", line: spinner.row)
+      spinner.spin
+    end
+  end
+end
+
+threads.each(&:join)