fix: Icon is required for the web version.

[DavidHHDS]

Without icon the plugin cannot be loaded in the web version.

[learn-build-service-prod[bot]]

Learn Build status updates of commit c233b57:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
docs/manifest/item.md	:white_check_mark:Succeeded	View (>=common-js || >=outlook-js-1.1 || >=excel-js-1.1 || onenote-js-1.1 || >=powerpoint-js-1.1 || visio-js-1.1 || >=word-js-1.1)

For more details, please refer to the build report.

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[AlexJerabek]

Hi @DavidHHDS,

Thank you for reporting this and proposing a documentation fix. @samantharamon, could you please confirm?