chore: adding intro strings workshop

[jdwilkin4]

Summary

This will be the intro strings workshop at the beginning of the the JavaScript strings module.

It covers the following:

• const
• assignment
• string concatenation using the + operator
• template literals
• str.length property
• bracket notation and retrieving characters from strings
• str.indexOf method

Checklist:

• [x] I have read freeCodeCamp's contribution guidelines.
• [x] My pull request has a descriptive title (not a vague title like Update index.md)

Closes #414

[jdwilkin4]

Yeah, we can put some of these into variables and just log the variable. It will be easier to test that way to