Write inline documentation for js/src/threepio.js

[tcp]

Where?

js/src/threepio.js

Who?

Any developer who wants to work on Threepio should be able to read inline documentation for this file, as well as any file in the project.

What?

We need to go "line-by-line" and create inline documentation for this file. Please try to use proper punctuation and English grammar to the best of your ability.

Additional Context

None

[ShubhamChaudharyy]

can i take up this issue?