in markdown rendering, add missing space-lines which are in-between comment lines

[daslu]

https://clojurians.zulipchat.com/#narrow/stream/422115-clay-dev/topic/Enumeration.20separation/near/419421288

The two following namespace examples should be rendered the same:

(ns my-namespace)
;; some text

;; - first point
;; - second

(ns my-namespace)
;; some text
;;
;; - first point
;; - second

edit: fixed example