Update sage tutorial

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Component: **documentation**

Author: **Kwankyu Lee**

Branch/Commit: **[`bb42d88`](https://github.com/sagemath/sagetrac-mirror/commit/bb42d889e2647edbe74dd3598d0dd5aafc9a97fe)**

Reviewer: **Eric Gourgoulhon**

_Issue created by migration from https://trac.sagemath.org/ticket/34751_

