[3.13] For-else deserves its own section in the tutorial (GH-123946) (#124564)

For-else deserves its own section in the tutorial (GH-123946)

* For-else deserves its own section in the tutorial

* remove mention of unrolling the loop

* Update Doc/tutorial/controlflow.rst



---------

(cherry picked from commit ffdc80e93d9d947531fa0123e5b392c6f1fd9136)

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>