Add Pretend Generations as a rails til.

README.md

@@ -55,6 +55,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Capybara Page Status Code](rails/capybara-page-status-code.md)
 - [Conditional Class Selectors in Haml](rails/conditional-class-selectors-in-haml.md)
 - [Creating Records of Has_One Associations](rails/creating-records-of-has-one-associations.md)
+- [Pretend Generations](rails/pretend-generations.md)
 - [Show Pending Migrations](rails/show-pending-migrations.md)
 
 ### ruby

rails/pretend-generations.md

@@ -0,0 +1,24 @@
+# Pretend Generations
+
+To get an idea of what a `rails generate` command is going to to
+*generate*, you can do a dry run with the `-p` flag or
+the `--pretend` flag. If you run
+
+```
+$ rails generate model post -p
+```
+
+then you will see the following output
+
+```
+    invoke  active_record
+    create    db/migrate/20150513132556_create_posts.rb
+    create    app/models/post.rb
+    invoke    rspec
+    create      spec/models/post_spec.rb
+    invoke      factory_girl
+    create        spec/factories/posts.rb
+```
+
+though those files will not have actually been created. You now know
+precisely what rails will generate for you.