help: clarify the unit of `ui.large-file-limit` config stable

help: clarify the unit of `ui.large-file-limit` config

Its might be a bit confusing, especially since `large-file.min-size` uses MB.

Differential Revision: https://phab.mercurial-scm.org/D12483

--- a/mercurial/helptext/config.txt	Wed Apr 06 18:39:15 2022 +0200
+++ b/mercurial/helptext/config.txt	Thu Apr 07 15:46:07 2022 +0200
@@ -2630,7 +2630,8 @@
 ``large-file-limit``
     Largest file size that gives no memory use warning.
     Possible values are integers or 0 to disable the check.
-    (default: 10000000)
+    Value is expressed in bytes by default, one can use standard units for
+    convenience (e.g. 10MB, 0.1GB, etc) (default: 10000000)
 
 ``logtemplate``
     (DEPRECATED) Use ``command-templates.log`` instead.