helptext: mention in `hg help config` that `.hg/hgrc-not-shared` is consulted
Recently we added `.hg/hgrc-not-shared` which is a config file which won't be
shared with shares when share-safe mode is enabled. Irrespective of whether
we are using share-safe or not, we consult this file now.
Let's document that.
Differential Revision: https://phab.mercurial-scm.org/D9412
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true