docs: clarify case-sensitive value check for highest-available-docume…

[mithilP007]

…nt-mode

Fixes #3506

Added a clear note in the "What does the hint check?" section to inform users that the value check is case-sensitive (ie=edge vs IE=edge). This addresses the confusion mentioned in issue #3506 where the case-sensitivity requirement was buried in the configuration section and not immediately obvious to users.

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• :white_check_mark: login: mithilP007 / name: Manjiro Sano (72e63317b68d30857369e6a4e12ff6667ff36b95)