DEV: Add short explanations for the core features specs (#78)

Author: Flink

spec/system/core_features_spec.rb

@@ -1,5 +1,13 @@
 # frozen_string_literal: true
 
+# Parts of the core features examples can be skipped like so:
+#   it_behaves_like "having working core features", skip_examples: %i[login likes]
+#
+# List of keywords for skipping examples:
+# login, likes, profile, topics, topics:read, topics:reply, topics:create,
+# search, search:quick_search, search:full_page
+#
+# For more details, see https://meta.discourse.org/t/-/361381
 RSpec.describe "Core features", type: :system do
   before { enable_current_plugin }