Introduce issue templates (#22)

Based on #21 from @choosen

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,57 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+### Basic Version Info
+Faraday Version: X.Y.Z
+Ruby Version: X.Y.Z
+
+### Issue description
+<!-- Tell us what's wrong -->
+
+### Actual behavior
+<!-- Tell us what should happen -->
+
+### Expected behavior
+<!-- Tell us what should happen -->
+
+### Steps to reproduce
+
+```ruby
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require "bundler/inline"
+
+gemfile do
+  source "https://rubygems.org"
+
+  gem "faraday"
+  gem "faraday-retry"
+end
+
+count = 0
+expected = 5
+retry_options = {
+  max: expected,
+  interval: 0.1,
+  retry_statuses: [503],
+  retry_block: proc { count += 1 }
+}
+
+faraday = Faraday.new do |conn|
+  conn.request :retry, **retry_options
+end
+
+faraday.get("https://httpbin.org/status/503")
+
+exit 0 if count == expected
+
+warn "Retried #{count} times, expected #{expected}"
+exit 1
+```