Add doc for Generating RBS

docs/data_and_struct.md

@@ -55,3 +55,32 @@ Measure.ancestors #=> [Measure, #<Class:0xOOF>, Data, ...]
 ```
 
 [^1]: [Shannon Skipper](https://github.com/havenwood) told me it in Discord
+
+## Generate prototype for `Data` and `Struct`
+
+RBS prototypes for classes using `Data` and `Struct` can be generated by `rbs prototype runtime`.
+
+```rb
+# t.rb
+class Measure < Data.define(:amount, :unit)
+end
+```
+
+```
+$ bundle exec rbs prototype runtime -R t.rb Measure
+class Measure < ::Data
+  def self.new: (untyped amount, untyped unit) -> instance
+              | (amount: untyped, unit: untyped) -> instance
+
+  def self.[]: (untyped amount, untyped unit) -> instance
+             | (amount: untyped, unit: untyped) -> instance
+
+  def self.members: () -> [ :amount, :unit ]
+
+  def members: () -> [ :amount, :unit ]
+
+  attr_reader amount: untyped
+
+  attr_reader unit: untyped
+end
+```