hg: tune the [diff] config

hosts/common/programs/mercurial.nix

@@ -13,6 +13,8 @@
       "ref"
     ];
     fs.".config/hg/hgrc".symlink.text = ''
+      # `hg config` => to show the finalized config
+
       [extensions]
       # Mercurial Queues (MQ) extension adds patch-stack support to mercurial.
       # MQ is shipped in mercurial, but not enabled by default.
@@ -20,10 +22,11 @@
       mq =
 
       [diff]
-      # TODO: how much of this is default?
-      showfunc = True
+      # showfunc = True
+      # `diff.git = True`: render diffs with `diff --git` instead of `diff -r`
       git = True
-      unified = 10
+      # `diff.unified = N`: show N lines of context (else, use default as per `diff`)
+      # unified = 10
 
       [alias]
       q = qseries -s -v