Added tutorial - Recreacting the linux 'which' command in go - Beginner friendly tutorial

[AyoubIssaad]

Description

I'd like to contribute to the repo by adding my own tutorial (recreating the Linux which command in go), it's a beginner friendly detailed step by step guide to recreate the Linux 'which' command from scratch.

Motivation and Context

Hopefully this tutorial will help beginners get a fundamental understanding of some Go concepts in a practical, hands-on manner.

How Has This Been Tested? I wrote it myself.

Types of changes

• [x] New Article (change which adds functionality)

Checklist:

• [x] My code follows the code style of this project.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have made checks to ensure URLs and other resources are valid