Document value of a sequence can be any Enumerable

* Update GETTING_STARTED.md with mention Array#cycle
* Update GETTING_STARTED.md by move Array#cycle mention
* Remove unused TOC entry for GETTING_STARTED.md

Co-authored-by: Alexandr Borisov <ab@cifronomika.ru>

GETTING_STARTED.md

@@ -1013,6 +1013,15 @@ factory :post do
 end
 ```
 
+Please note, that the value for the sequence could be any Enumerable instance,
+as long as it responds to `#next`:
+
+```ruby
+factory :task do
+  sequence :priority, %i[low medium high urgent].cycle
+end
+```
+
 ### Aliases
 
 Sequences can also have aliases. The sequence aliases share the same counter: