tweaks

doc/source/ch08_csst_common.rst

@@ -153,13 +153,21 @@ here is the way to combine records:
     >>> fr2.add_record(filepath="test2.txt", db=False, comment="test file 2")
     >>> fr_all = FileRecorder([*fr1, *fr2])
     >>> fr_all.pprint_all()
-
     <FileRecorder length=2>
      filepath   db    comment   existence
     --------- ----- ----------- ---------
     test1.txt False test file 1     False
     test2.txt False test file 2     False
 
+    >>> fr_all.extend(fr1)
+    >>> fr_all.pprint_all()
+    <FileRecorder length=3>
+     filepath   db    comment   existence
+    --------- ----- ----------- ---------
+    test1.txt False test file 1     False
+    test2.txt False test file 2     False
+    test1.txt False test file 1     False
+
 
 ``csst_common.logger.get_logger()``
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