Use "adoc" extension for asciidoc, it's the GitLab convention.

advent.adoc

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+= advent(6) =
+:doctype: manpage
+
+== NAME ==
+advent - Colossal Cave Adventure
+
+== SYNOPSIS ==
+*advent* [-l logfile] [-o]
+
+== DESCRIPTION ==
+The original Colossal Cave Adventure from 1976 was the origin of all
+text adventures, dungeon-crawl (computer) games, and computer-hosted
+roleplaying games.
+
+This is the last version released by Crowther & Woods, its original
+authors, in 1995.  It has been known as "adventure 2.5" and "430-point
+adventure".  To learn more about the changes since the 350-point
+original, type 'news' at the command prompt.
+
+There is an 'adventure' in the BSD games package that is a C port by
+Jim Gillogly of the 1976 ancestor of this game.  To avoid a name
+collision, this game builds as 'advent', reflecting the fact that the
+PDP-10 on which it originally ran limited filenames to 6 characters.
+
+This version is released as open source with the permission and
+encouragement of the original authors.
+
+== OPTIONS ==
+
+-l:: Log commands to specified file.
+
+-o:: Old-style.  Restores original interface, no prompt.
+
+== REPORTING BUGS ==
+Report bugs to Eric S. Raymond <esr@thyrsus.com>.  The project page is
+at http://catb.org/~esr/advent
+
+== SEE ALSO ==
+wumpus(6), adventure(6), zork(6), rogue(6), nethack(6).