User guide KB docs

(Not a bug but something needs to be pointed out in the article.)

Specifically this article:

https://www.phpbb.com/support/docs/en/3.1/kb/article/using-bigdump-to-restore-large-database-dumps/

its not to be used under PHP7. As bigdump script is NO longer supported (ABD) and most importantly it does NOT work for PHP7.

Dave