Update auto-generated docs

manual/cops_rails.md

@@ -804,6 +804,43 @@ Include | `app/models/**/*.rb` | Array
 
 * [https://github.com/rubocop-hq/rails-style-guide#has_many-has_one-dependent-option](https://github.com/rubocop-hq/rails-style-guide#has_many-has_one-dependent-option)
 
+## Rails/HelperInstanceVariable
+
+Enabled by default | Supports autocorrection
+--- | ---
+Enabled | No
+
+This cop checks for use of the helper methods which reference
+instance variables.
+
+Relying on the existing of a particular instance variable
+makes it difficult to re-use helper methods in different
+contexts.
+
+If it seems awkward to explicitly pass in each dependent
+variable, consider moving the behaviour elsewhere, for
+example to a model, decorator or presenter.
+
+### Examples
+
+```ruby
+# bad
+def welcome_message
+  "Hello " + @user.name
+end
+
+# good
+def welcome_message(user)
+  "Hello " + user.name
+end
+```
+
+### Configurable attributes
+
+Name | Default value | Configurable values
+--- | --- | ---
+Include | `app/helpers/**/*.rb` | Array
+
 ## Rails/HttpPositionalArguments
 
 Enabled by default | Supports autocorrection