It should be available in free account.It doesnt make sense not to have customer define the description.At least customer should be able to remove the default string which shows up  "Enter forum description here ..."
Got the answer! The option is available as mentioned by sergey on an earlier post!

Sergey Stukov
Answer Answered
Default string displayed only to admins.

Setting description available in the free plan.


and then click setup action on description block
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