Document how to extend bots locally.

Close #536.

README.md

@@ -322,6 +322,14 @@ Browser::Bot.matchers.delete(Browser::Bot::KeywordMatcher)
 Browser::Bot.matchers.delete(Browser::Bot::EmptyUserAgentMatcher)
 ```
 
+To extend the bot list, you can manipulate the methods below:
+
+```ruby
+Browser::Bot.bots.merge!(new_bots_hash)
+Browser::Bot.bot_exceptions += new_exceptions
+Browser::Bot.search_engines.merge!(new_search_engines_hash)
+```
+
 ### Middleware
 
 You can use the `Browser::Middleware` to redirect user agents.

search_engines.yml

@@ -1,3 +1,4 @@
+---
 ask jeeves: "Ask Jeeves"
 baidu: "Chinese search engine"
 bingbot: "Microsoft bing bot"

test/unit/bots_test.rb

@@ -108,4 +108,15 @@ class BotsTest < Minitest::Test
       assert_equal Browser::Bot::KeywordMatcher, browser.bot.why?
     end
   end
+
+  test "extends lists" do
+    Browser::Bot.bots["another-bot"] = "Another bot"
+    Browser::Bot.bot_exceptions.push("exclude-this-bot")
+    Browser::Bot.search_engines["new-search-engine"] = "New search engine"
+
+    assert_equal "Another bot", Browser::Bot.bots["another-bot"]
+    assert_includes Browser::Bot.bot_exceptions, "exclude-this-bot"
+    assert_equal "New search engine",
+                 Browser::Bot.search_engines["new-search-engine"]
+  end
 end