subrepo: update help for commit to reflect new default behavior

Update the subrepo help to be consistent with the new default behavior,
which is to abort if any subrepo is dirty.

mercurial/help/subrepos.txt

@@ -80,12 +80,13 b' Interaction with Mercurial Commands'
     -S/--subrepos is specified.
 
 :commit: commit creates a consistent snapshot of the state of the
-    entire project and its subrepositories. It does this by first
-    attempting to commit all modified subrepositories, then recording
-    their state and finally committing it in the parent
-    repository. Mercurial can be made to abort if any subrepository
-    content is modified by setting "ui.commitsubrepos=no" in a
-    configuration file (see :hg:`help config`).
+    entire project and its subrepositories. If any subrepositories
+    have been modified, Mercurial will abort.  Mercurial can be made
+    to instead commit all modified subrepositories by specifying
+    -S/--subrepos, or setting "ui.commitsubrepos=True" in a
+    configuration file (see :hg:`help config`).  After there are no
+    longer any modified subrepositories, it records their state and
+    finally commits it in the parent repository.
 
 :diff: diff does not recurse in subrepos unless -S/--subrepos is
     specified. Changes are displayed as usual, on the subrepositories