Added description for ADT and SST

[minniewong]

Description

Added a description for Absolute Dynamic Topography and GHRSST SST.

Checklist

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• I have read the CONTRIBUTING doc
• I have added necessary documentation (if appropriate)
• I have added tests that prove my fix is effective or that my feature works
• Lint and unit tests pass locally with my changes (npm run test)
• Any dependent changes have been merged and published in downstream modules

Further comments

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@nasa-gibs/worldview

[ZachTRice]

👍