[PATCH 2 of 4 STABLE V3] pager: document the 'pager.enable' option

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at ens-lyon.org>
# Date 1493649823 -7200
#      Mon May 01 16:43:43 2017 +0200
# Branch stable
# Node ID 8308b782037b7026adec025886829c6f8cbd6c16
# Parent  505986a1a595d39cb7cf6f74e3862bf297a07072
# EXP-Topic pager
# Available At https://www.mercurial-scm.org/repo/users/marmoute/mercurial/
#              hg pull https://www.mercurial-scm.org/repo/users/marmoute/mercurial/ -r 8308b782037b
pager: document the 'pager.enable' option

The 'config' helps was missing help about pager enabling/disabling.

diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
--- a/mercurial/help/config.txt
+++ b/mercurial/help/config.txt
@@ -1367,6 +1367,9 @@ Supported arguments:
 Setting used to control when to paginate and with what external tool. See
 :hg:`help pager` for details.
 
+``enable``
+  Control the pagination of command output (default: True).
+
 ``pager``
     Define the external tool used as pager.