Add explanation why RSpec/DescribedClass autocorrection is unsafe

Author: lovro-bikic

docs/modules/ROOT/pages/cops_rspec.adoc

@@ -985,6 +985,13 @@ To narrow down this setting to only a specific directory, it is
 possible to use an overriding configuration file local to that
 directory.
 
+[#safety-rspecdescribedclass]
+=== Safety
+
+Autocorrection is unsafe when `SkipBlocks: false` because
+`described_class` might not be available within the block (for
+example, in rspec-rails's `controller` helper).
+
 [#examples-rspecdescribedclass]
 === Examples
 

lib/rubocop/cop/rspec/described_class.rb

@@ -13,6 +13,20 @@ module RSpec
       # `OnlyStaticConstants` is only relevant when `EnforcedStyle` is
       # `described_class`.
       #
+      # There's a known caveat with rspec-rails's `controller` helper that
+      # runs its block in a different context, and `described_class` is not
+      # available to it. `SkipBlocks` option excludes detection in all
+      # non-RSpec related blocks.
+      #
+      # To narrow down this setting to only a specific directory, it is
+      # possible to use an overriding configuration file local to that
+      # directory.
+      #
+      # @safety
+      #   Autocorrection is unsafe when `SkipBlocks: false` because
+      #   `described_class` might not be available within the block (for
+      #   example, in rspec-rails's `controller` helper).
+      #
       # @example `EnforcedStyle: described_class` (default)
       #   # bad
       #   describe MyClass do
@@ -47,15 +61,6 @@ module RSpec
       #     subject { MyClass.do_something }
       #   end
       #
-      # There's a known caveat with rspec-rails's `controller` helper that
-      # runs its block in a different context, and `described_class` is not
-      # available to it. `SkipBlocks` option excludes detection in all
-      # non-RSpec related blocks.
-      #
-      # To narrow down this setting to only a specific directory, it is
-      # possible to use an overriding configuration file local to that
-      # directory.
-      #
       # @example `SkipBlocks: true`
       #   # spec/controllers/.rubocop.yml
       #   # RSpec/DescribedClass: