add echo bot README.md

Author: 4geru

examples/echobot/Gemfile

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
+
+gem 'sinatra'
+gem 'line-bot-api'

examples/echobot/README.md

@@ -0,0 +1,16 @@
+# Echo Bot
+
+An example LINE bot just to echo messages
+
+## Getting started
+
+```ruby
+$ export LINE_CHANNEL_SECRET=YOUR_CHANNEL_SECRET
+$ export LINE_CHANNEL_TOKEN=YOUR_CHANNEL_ACCESS_TOKEN
+$ bundle install
+$ bundle exec ruby app.rb
+```
+
+```
+https://your.base.url:4567/callback
+```