Added tutorial - 4 javascript tutorials

[Aarghyadeep]

Description

I added four tutorials -

1. Build a simple URL shortener with javascript.
2. Build a memory game in javascript.
3. Build a count-down timer with javascript.
4. Build a digital javascript drum kit.

Motivation and Context

I found there were very few javascript tutorials. Since it is a very important language in web dev category so I decided to add more tutorials which are really fun and interesting.

How Has This Been Tested?

I have checked the typo and also whether the links are working or not.

Types of changes

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

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