add chinese for pages.cn/linux/add-apt-respository.md

pages.cn/common/gnuplot.md

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+# gnuplot
+
+> A graph plotter that outputs in several formats.
+
+- Start the interactive graph plotting shell:
+
+`gnuplot`
+
+- Plot the graph for the specified graph definition file:
+
+`gnuplot {{path/to/definition.plt}}`
+
+- Set the output format by executing a command before loading the definition file:
+
+`gnuplot -e "{{set output "path/to/filename.png" size 1024,768}}" {{path/to/definition.plt}}`
+
+- Persist the graph plot preview window after gnuplot exits:
+
+`gnuplot --persist {{path/to/definition.plt}}`