Stop using changelog file

Author: uniwix

README.rst

@@ -64,7 +64,7 @@ Nothing needed.
 Release history
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-See `CHANGELOG.md <https://github.com/uniwix/casioplot/blob/master/CHANGELOG.md>`_.
+See `Github release page <https://github.com/uniwix/casioplot/releases>`_.
 
 Meta
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