Missing documentation for User Defined Wind in InflowWind

[deslaughter]

Bug description <A clear and concise description of the bug.>

OpenFAST documentation hasn't been updated to explain how to use the user defined wind as part of the Flow Field code organization. This applies to main, dev, and dev-tc branches and needs to be fixed for the 4.2 release.

See thread at https://forums.nrel.gov/t/user-defined-windtype-in-inflowwind/9296 for relevant details.