[Feature] Add Javascript Licenses

[ncorder]

Feature: Add LibreJS compliant JS formats.

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[ncorder]

I have some experience with JS, and am attempting to properly locate all scripts in the repository.

Where is the JS mdBook uses located? I noticed there weren't any .js files in the directory and want to make sure I am indeed in the right place.

[ISSOtm]

Those in src/theme/.