Update knowledge/how to use nodejs repl (#2156)
Update knowledge/how to use nodejs repl (#2156)

1. Updated code blocks to fences, added shell syntax.
2. Added headers to sections
3. Added "Special Commands" section, from the Node API docs
Mention the existence of built in REPL module and standalone executable
yous/new.nodejs.org,phillipj/new.nodejs.org,nodejs/new.nodejs.org,nodejs/new.nodejs.org,yous/new.nodejs.org,phillipj/new.nodejs.org