Merge pull request #4600 from MichaelEischer/doc-forget-note-1

Add a note that the oldest snapshot may be kept additionally

doc/060_forget.rst

@@ -207,10 +207,13 @@ The ``forget`` command accepts the following policy options:
     They also only count hours/days/weeks/etc which have one or more snapshots.
     A value of ``-1`` will be interpreted as "forever", i.e. "keep all".
 
-.. note:: All duration related options (``--keep-{within,-*}``) ignore snapshots
+.. note:: All duration related options (``--keep-{within-,}*``) ignore snapshots
     with a timestamp in the future (relative to when the ``forget`` command is
     run) and these snapshots will hence not be removed.
 
+.. note:: If there are not enough snapshots to keep one for each duration related
+    ``--keep-{within-,}*`` option, the oldest snapshot is kept additionally.
+
 .. note:: Specifying ``--keep-tag ''`` will match untagged snapshots only.
 
 When ``forget`` is run with a policy, restic first loads the list of all snapshots