Add example database.yml and update README

Author: mhartl

README.md

@@ -7,6 +7,7 @@ by [Michael Hartl](http://michaelhartl.com/). You can use this reference impleme
     $ cd /tmp
     $ git clone git@github.com:railstutorial/sample_app_2nd_ed.git
     $ cd sample_app_2nd_ed
+    $ cp config/database.yml.example config/database.yml
     $ bundle install
     $ bundle exec rake db:migrate
     $ bundle exec rake db:test:prepare

config/database.yml.example

@@ -0,0 +1,28 @@
+# SQLite version 3.x
+#   gem install sqlite3
+#
+#   Ensure the SQLite 3 gem is defined in your Gemfile
+#   gem 'sqlite3'
+development:
+  adapter: sqlite3
+  database: db/development.sqlite3
+  pool: 5
+  timeout: 5000
+
+# Warning: The database defined as "test" will be erased and
+# re-generated from your development database when you run "rake".
+# Do not set this db to the same as development or production.
+test: &test
+  adapter: sqlite3
+  database: db/test.sqlite3
+  pool: 5
+  timeout: 5000
+
+production:
+  adapter: sqlite3
+  database: db/production.sqlite3
+  pool: 5
+  timeout: 5000
+
+cucumber:
+  <<: *test