Add format vs interpolation

format-string/README.md

@@ -0,0 +1,12 @@
+```
+Warming up --------------------------------------
+              format   611.664k i/100ms
+                 #{}     1.229M i/100ms
+Calculating -------------------------------------
+              format      6.037M (± 4.3%) i/s -     30.583M in   5.077835s
+                 #{}     12.277M (± 0.4%) i/s -     61.438M in   5.004388s
+
+Comparison:
+                 #{}: 12276995.7 i/s
+              format:  6037136.3 i/s - 2.03x  slower
+```

format-string/example.rb

@@ -0,0 +1,16 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require 'benchmark/ips'
+
+value = 'value'
+
+Benchmark.ips do |x|
+  x.time = 5
+  x.warmup = 0.5
+
+  x.report('format') { format('key:%s', value) }
+  x.report('#{}') { "key:#{value}" }
+
+  x.compare!
+end