Document that Ruby Hashes in lazy attributes need double curly brackets

Closes #854

GETTING_STARTED.md

@@ -162,6 +162,15 @@ factory :user do
 end
 ```
 
+Because of the block syntax in Ruby, defining attributes as `Hash`es (for
+serialized/JSON columns, for example) requires two sets of curly brackets:
+
+```ruby
+factory :program do
+  configuration { { auto_resolve: false, auto_define: true } }
+end
+```
+
 Aliases
 -------