Improve Tool Tip docs when starting from Scratch

[roblabs]

While building a style from Scratch, I wasn't sure what this tool tip meant.

• 'source map data link (if available)'

I believe it is looking for a URL to a TileJSON. If correct, should it have a suggested URL such as http://localhost:8081/path/to/tileJson.json

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Source

fresco/src/component/StyleAdd/StyleAddScratch.jsx

Line 86 in ee65f3d

info={'source map data link (if available)'}

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