Clarify license upload directions in the doc

What does this MR do and why?

As @stanhu noted in Slack, the license upload direction in the License documentation was missing some specification. The instructions directed users to select Menu > Admin from the top bar, then on the left sidebar select Settings, but didn't mention to use the General section. General is the first/default section but we should call this out specifically to avoid confusion.

This MR updates the docs to make it clear which section to find the license upload page.

Screenshots or screen recordings

For reference, here's where the license upload page can be found:

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