docs(bash): add bash learning resources

[AKakshaypratap]

Description

Motivation and Context

How Has This Been Tested?

Types of changes

• Content Update (change which fixes an issue or updates an already existing submission)
• New Article (change which adds functionality)
• Documentation change

Checklist:

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

[tuvtran]

Thanks for the contribution. This list is specifically for free tutorials where the reader builds a concrete project from scratch — 'Learn Bash the Hard Way' is a Leanpub book sales page, and the TLDP Bash Guide is a general reference guide rather than a project-based tutorial, so they don't quite fit here. Also note the new section was inserted above the README title, which breaks the page layout; if you find a free, project-based Bash tutorial in the future, we'd be happy to see another PR.