Add practice exercise Rail Fence Cipher

[klimkin]

No description provided.

[github-actions]

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[vaeng]

@klimkin
Hey, thanks for your effort. Can you correct the errors that were raised by the checks?

[vaeng]

@klimkin
Do you want help with the results of the checks, or can you manage by yourself?

[klimkin]

@klimkin Do you want help with the results of the checks, or can you manage by yourself?

If it still fails after the latest commit, I could use some help. Thank you!

[vaeng]

All checks pass. Congrats on your submission!