Add missing file doc/argument_io.rdoc (#140)

BurdetteLamar · web-flow · commit e37f04aa5cb4 · 2020-06-16T06:43:36.000+09:00
diff --git a/doc/argument_io.rdoc b/doc/argument_io.rdoc
@@ -0,0 +1,5 @@
+* Argument +io+ should be an IO object that is:
+  * Open for reading; on return, the IO object will be closed.
+  * Positioned at the beginning.
+    To position at the end, for appending, use method CSV.generate.
+    For any other positioning, pass a preset \StringIO object instead.
